Method and apparatus for improving retransmission scheduling of sidelink communication in a wireless communication system

ABSTRACT

Methods and apparatuses for improving retransmission scheduling of sidelink communications are disclosed herein. In one method, a first device monitors a down control signal for scheduling sidelink resource. The first device performs a sidelink transmission for a second device based on a first sidelink grant allocated by a base station. The first device determines a retransmission need of the sidelink transmission based on a Hybrid Automatic Repeat Request (HARQ) feedback of the sidelink transmission from the second device. The first device transmits a retransmission indication for the retransmission need to the base station. The first device starts or restarts a timer upon the transmission of the retransmission indication, wherein the timer is used for controlling a period of monitoring a downlink control resource set.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present Application is a continuation of U.S. patent applicationSer. No. 16/797,577, filed Feb. 21, 2020, which claims priority to andthe benefit of U.S. Provisional Patent Application Ser. No. 62/808,482,filed Feb. 21, 2019; with the entire disclosures of each referencedapplication fully incorporated herein by reference.

FIELD

This disclosure generally relates to wireless communication networks,and more particularly, to a method and apparatus for improvingretransmission scheduling of sidelink communication in a wirelesscommunication system.

BACKGROUND

With the rapid rise in demand for communication of large amounts of datato and from mobile communication devices, traditional mobile voicecommunication networks are evolving into networks that communicate withInternet Protocol (IP) data packets. Such IP data packet communicationcan provide users of mobile communication devices with voice over IP,multimedia, multicast and on-demand communication services.

An exemplary network structure is an Evolved Universal Terrestrial RadioAccess Network (E-UTRAN). The E-UTRAN system can provide high datathroughput in order to realize the above-noted voice over IP andmultimedia services. A new radio technology for the next generation(e.g., 5G) is currently being discussed by the 3GPP standardsorganization. Accordingly, changes to the current body of 3GPP standardare currently being submitted and considered to evolve and finalize the3GPP standard.

SUMMARY

In one method, a first device monitors a down control signal forscheduling sidelink resource. The first device performs a sidelinktransmission for a second device based on a first sidelink grantallocated by a base station. The first device determines aretransmission need of the sidelink transmission based on a HybridAutomatic Repeat Request (HARQ) feedback of the sidelink transmissionfrom the second device. The first device transmits a retransmissionindication for the retransmission need to the base station. The firstdevice starts or restarts a timer upon the transmission of theretransmission indication, wherein the timer is used for controlling aperiod of monitoring a downlink control resource set.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram of a wireless communication system according toone exemplary embodiment.

FIG. 2 is a block diagram of a transmitter system (also known as accessnetwork) and a receiver system (also known as user equipment or UE)according to one exemplary embodiment.

FIG. 3 is a functional block diagram of a communication system accordingto one exemplary embodiment.

FIG. 4 is a functional block diagram of the program code of FIG. 3according to one exemplary embodiment.

FIG. 5 is a reproduction of FIG. 6.1.3.1 a-1 showing Sidelink BSR andTruncated Sidelink BSR MAC control element for even N taken from 3GPP TS36.321-f30.

FIG. 6 is a reproduction of FIG. 6.1.3.1 a-2: Sidelink BSR and TruncatedSidelink BSR MAC control element for odd N taken from 3GPP TS36.321-f30.

FIG. 7 is a reproduction of FIG. 6.1.6-1 showing R/R/E/LCID/F/L MACsubheader taken from 3GPP TS 36.321-f30.

FIG. 8 is a reproduction of FIG. 6.1.6-2 showing R/R/E/LCID MACsubheader taken from 3GPP TS 36.321-f30.

FIG. 9 is a reproduction of FIG. 6.1.6-3 showing SL-SCH MAC subheaderfor V=“0001” and “0010” taken from 3GPP TS 36.321-f30.

FIG. 10 is a reproduction of FIG. 6.1.6-3 a showing SL-SCH MAC subheaderfor V=″0011″ taken from 3GPP TS 36.321-f30.

FIG. 11 is a reproduction of FIG. 6.1.6-4 showing an “Example of MAC PDUconsisting of MAC header, MAC SDUs and padding” taken from 3GPP TS36.321-f30.

FIG. 12 illustrates an issue of NR V2X sidelink with DRX.

FIG. 13 illustrates one exemplary embodiment showing a long enoughinactivity timer.

FIG. 14 illustrates one exemplary embodiment showing a start or restartof an inactivity timer for transmitting a feedback of a sidelinktransmission to BS.

FIG. 15 is a flow diagram for one exemplary embodiment from theperspective of a User Equipment (UE).

DETAILED DESCRIPTION

The exemplary wireless communication systems and devices described belowemploy a wireless communication system, supporting a broadcast service.Wireless communication systems are widely deployed to provide varioustypes of communication such as voice, data, and so on. These systems maybe based on code division multiple access (CDMA), time division multipleaccess (TDMA), orthogonal frequency division multiple access (OFDMA),3GPP LTE (Long Term Evolution) wireless access, 3GPP LTE-A orLTE-Advanced (Long Term Evolution Advanced), 3GPP2 UMB (Ultra MobileBroadband), WiMax, 3GPP NR (New Radio) wireless access for 5G, or someother modulation techniques.

In particular, the exemplary wireless communication systems devicesdescribed below may be designed to support one or more standards such asthe standard offered by a consortium named “3rd Generation PartnershipProject” referred to herein as 3GPP, including: TS 36.321-f30; RAN1 #94chairman's note; TS 38.321-f40; TS 38.321-f40; and RAN1 #adhoc1901Chairman's Note. The standards and documents listed above are herebyexpressly incorporated by reference in their entirety.

FIG. 1 shows a multiple access wireless communication system accordingto one embodiment of the invention. An access network 100 (AN) includesmultiple antenna groups, one including 104 and 106, another including108 and 110, and an additional including 112 and 114. In FIG. 1, onlytwo antennas are shown for each antenna group, however, more or fewerantennas may be utilized for each antenna group. Access terminal 116(AT) is in communication with antennas 112 and 114, where antennas 112and 114 transmit information to access terminal 116 over forward link120 and receive information from access terminal 116 over reverse link118. Access terminal (AT) 122 is in communication with antennas 106 and108, where antennas 106 and 108 transmit information to access terminal(AT) 122 over forward link 126 and receive information from accessterminal (AT) 122 over reverse link 124. In a FDD system, communicationlinks 118, 120, 124 and 126 may use different frequency forcommunication. For example, forward link 120 may use a differentfrequency then that used by reverse link 118.

Each group of antennas and/or the area in which they are designed tocommunicate is often referred to as a sector of the access network. Inthe embodiment, antenna groups each are designed to communicate toaccess terminals in a sector of the areas covered by access network 100.

In communication over forward links 120 and 126, the transmittingantennas of access network 100 may utilize beamforming in order toimprove the signal-to-noise ratio of forward links for the differentaccess terminals 116 and 122. Also, an access network using beamformingto transmit to access terminals scattered randomly through its coveragecauses less interference to access terminals in neighboring cells thanan access network transmitting through a single antenna to all itsaccess terminals.

An access network (AN) may be a fixed station or base station used forcommunicating with the terminals and may also be referred to as anaccess point, a Node B, a base station, an enhanced base station, anevolved Node B (eNB), a network node, a network, or some otherterminology. An access terminal (AT) may also be called user equipment(UE), a wireless communication device, terminal, access terminal or someother terminology.

FIG. 2 is a simplified block diagram of an embodiment of a transmittersystem 210 (also known as the access network) and a receiver system 250(also known as access terminal (AT) or user equipment (UE) in a MIMOsystem 200. At the transmitter system 210, traffic data for a number ofdata streams is provided from a data source 212 to a transmit (TX) dataprocessor 214.

In one embodiment, each data stream is transmitted over a respectivetransmit antenna. TX data processor 214 formats, codes, and interleavesthe traffic data for each data stream based on a particular codingscheme selected for that data stream to provide coded data.

The coded data for each data stream may be multiplexed with pilot datausing OFDM techniques. The pilot data is typically a known data patternthat is processed in a known manner and may be used at the receiversystem to estimate the channel response. The multiplexed pilot and codeddata for each data stream is then modulated (i.e., symbol mapped) basedon a particular modulation scheme (e.g., BPSK, QPSK, M-PSK, or M-QAM)selected for that data stream to provide modulation symbols. The datarate, coding, and modulation for each data stream may be determined byinstructions performed by processor 230.

The modulation symbols for all data streams are then provided to a TXMIMO processor 220, which may further process the modulation symbols(e.g., for OFDM). TX MIMO processor 220 then provides N_(T) modulationsymbol streams to N_(T) transmitters (TMTR) 222 a through 222 t. Incertain embodiments, TX MIMO processor 220 applies beamforming weightsto the symbols of the data streams and to the antenna from which thesymbol is being transmitted.

Each transmitter 222 receives and processes a respective symbol streamto provide one or more analog signals, and further conditions (e.g.,amplifies, filters, and upconverts) the analog signals to provide amodulated signal suitable for transmission over the MIMO channel. N_(T)modulated signals from transmitters 222 a through 222 t are thentransmitted from N_(T) antennas 224 a through 224 t, respectively.

At receiver system 250, the transmitted modulated signals are receivedby N_(R) antennas 252 a through 252 r and the received signal from eachantenna 252 is provided to a respective receiver (RCVR) 254 a through254 r. Each receiver 254 conditions (e.g., filters, amplifies, and downconverts) a respective received signal, digitizes the conditioned signalto provide samples, and further processes the samples to provide acorresponding “received” symbol stream.

An RX data processor 260 then receives and processes the N_(R) receivedsymbol streams from N_(R) receivers 254 based on a particular receiverprocessing technique to provide N_(T) “detected” symbol streams. The RXdata processor 260 then demodulates, deinterleaves, and decodes eachdetected symbol stream to recover the traffic data for the data stream.The processing by RX data processor 260 is complementary to thatperformed by TX MIMO processor 220 and TX data processor 214 attransmitter system 210.

A processor 270 periodically determines which pre-coding matrix to use(discussed below). Processor 270 formulates a reverse link messagecomprising a matrix index portion and a rank value portion.

The reverse link message may comprise various types of informationregarding the communication link and/or the received data stream. Thereverse link message is then processed by a TX data processor 238, whichalso receives traffic data for a number of data streams from a datasource 236, modulated by a modulator 280, conditioned by transmitters254 a through 254 r, and transmitted back to transmitter system 210.

At transmitter system 210, the modulated signals from receiver system250 are received by antennas 224, conditioned by receivers 222,demodulated by a demodulator 240, and processed by a RX data processor242 to extract the reserve link message transmitted by the receiversystem 250. Processor 230 then determines which pre-coding matrix to usefor determining the beamforming weights then processes the extractedmessage.

Turning to FIG. 3, this figure shows an alternative simplifiedfunctional block diagram of a communication device according to oneembodiment of the invention. As shown in FIG. 3, the communicationdevice 300 in a wireless communication system can be utilized forrealizing the UEs (or ATs) 116 and 122 in FIG. 1 or the base station (orAN) 100 in FIG. 1, and the wireless communications system is preferablythe LTE system or the NR system. The communication device 300 mayinclude an input device 302, an output device 304, a control circuit306, a central processing unit (CPU) 308, a memory 310, a program code312, and a transceiver 314. The control circuit 306 executes the programcode 312 in the memory 310 through the CPU 308, thereby controlling anoperation of the communications device 300. The communications device300 can receive signals input by a user through the input device 302,such as a keyboard or keypad, and can output images and sounds throughthe output device 304, such as a monitor or speakers. The transceiver314 is used to receive and transmit wireless signals, deliveringreceived signals to the control circuit 306, and outputting signalsgenerated by the control circuit 306 wirelessly. The communicationdevice 300 in a wireless communication system can also be utilized forrealizing the AN 100 in FIG. 1.

FIG. 4 is a simplified block diagram of the program code 312 shown inFIG. 3 in accordance with one embodiment of the invention. In thisembodiment, the program code 312 includes an application layer 400, aLayer 3 portion 402, and a Layer 2 portion 404, and is coupled to aLayer 1 portion 406. The Layer 3 portion 402 generally performs radioresource control. The Layer 2 portion 404 generally performs linkcontrol. The Layer 1 portion 406 generally performs physicalconnections.

Sidelink resource allocation and utilization mechanism in current MACspecification is disclosed in 3GPP TS36.321-f30 and is quoted below:

5.4.4 Scheduling Request

The Scheduling Request (SR) is used for requesting UL-SCH resources fornew transmission.When an SR is triggered, it shall be considered as pending until it iscancelled. All pending SR(s) shall be cancelled and sr-ProhibitTimer andssr-ProhibitTimer shall be stopped when a MAC PDU is assembled and thisPDU includes a BSR which contains buffer status up to (and including)the last event that triggered a BSR (see subclause 5.4.5), or, if allpending SR(s) are triggered by Sidelink BSR, when a MAC PDU is assembledand this PDU includes a Sidelink BSR which contains buffer status up to(and including) the last event that triggered a Sidelink BSR (seesubclause 5.14.1.4), or, if all pending SR(s) are triggered by SidelinkBSR, when upper layers configure autonomous resource selection, or whenthe UL grant(s) can accommodate all pending data available fortransmission.If the MAC entity has resources for SR configured on only one of SPUCCHand PUCCH, that SR resource is valid for all logical channels. If theMAC entity has resources for SR configured on both PUCCH and SPUCCH, MACentity shall consider all logical channels that have triggered an SR(and at retxBSR-Timer expiry, MAC entity shall consider all logicalchannels, belonging to a LCG, with data available for transmission):

-   -   PUCCH resources for SR are valid if logicalChannelSr-Restriction        is not configured, or if logical ChannelSr-Restriction allows SR        on PUCCH, for any of the logical channels;    -   SPUCCH resources for SR are valid if        logicalChannelSr-Restriction is not configured, or if        logicalChannelSr-Restriction allows SR on SPUCCH, for any of the        logical channels.        If an SR is triggered and there is no other SR pending, the MAC        entity shall set the SR_COUNTER and the SSR_COUNTER to 0.        As long as one SR is pending, the MAC entity shall for each TTI:    -   if no UL-SCH resources are available for a transmission in this        TTI:        -   Except for NB-IoT:            -   if the MAC entity has no valid PUCCH nor valid SPUCCH                resource for SR configured in any TTI:            -   if the MAC entity is a MCG MAC entity and rach-Skip is                not configured; or            -   if the MAC entity is a SCG MAC entity and rach-SkipSCG                is not configured:                -   initiate a Random Access procedure (see subclause                    5.1) on the corresponding SpCell and cancel all                    pending SRs;            -   else if this TTI is not part of a measurement gap or                Sidelink Discovery Gap for Transmission, and if                transmission of V2X sidelink communication is not                prioritized in this TTI as described in subclause                5.14.1.2.2:            -   if the MAC entity has at least one valid SPUCCH resource                for SR configured for this TTI and if ssr-ProhibitTimer                is not running:                -   if SSR_COUNTER<dssr-TransMax:                -    increment SSR_COUNTER by 1;                -    instruct the physical layer to signal the SR on one                    valid SPUCCH resource for SR;                -    start the ssr-ProhibitTimer.                -   else:                -    notify RRC to release SPUCCH for all serving cells;                -    if the MAC entity has no valid PUCCH resource for                    SR configured in any TTI:                -    notify RRC to release PUCCH for all serving cells;                -    notify RRC to release SRS for all serving cells;                -    clear any configured downlink assignments and                    uplink grants;                -    initiate a Random Access procedure (see subclause                    5.1) on the SpCell and cancel all pending SRs.            -   if the MAC entity has at least one valid PUCCH resource                for SR configured for this TTI and if sr-ProhibitTimer                is not running:                -   if SR_COUNTER<dsr-TransMax:                -    increment SR_COUNTER by 1;                -    instruct the physical layer to signal the SR on one                    valid PUCCH resource for SR;                -    start the sr-ProhibitTimer.                -   else:                -    notify RRC to release PUCCH and SPUCCH for all                    serving cells;                -    notify RRC to release SRS for all serving cells;                -    clear any configured downlink assignments and                    uplink grants;                -    initiate a Random Access procedure (see subclause                    5.1) on the SpCell and cancel all pending SRs.        -   For NB-IoT:            -   if the MAC entity has no valid resource for SR together                with acknowledgement of the data in this TTI and no                valid PRACH resource for SR configured in any TTI:            -   initiate a Random Access Procedure (see subclause 5.1)                and cancel all pending SRs.            -   else:            -   if the MAC entity has valid resource for SR together                with acknowledgement of the data in this TTI:                -   instruct the physical layer to signal the SR                    together with acknowledgement of the data.            -   else:                -   if the MAC entity has valid PRACH resource for SR                    configured in this TTI and sr-ProhibitTimer is not                    running:                -    instruct the physical layer to signal the SR on one                    valid PRACH resource for SR.                -    start the sr-ProhibitTimer in the subframe                    containing the last repetition of the corresponding                    SR transmission.            -   NOTE 1: The selection of which valid PUCCH/SPUCCH                resource for SR to signal SR on when the MAC entity has                more than one valid PUCCH/SPUCCH resource for SR in one                TTI or overlapping TTIs is left to UE implementation.            -   NOTE 2: SR_COUNTER is incremented for each SR bundle.                sr-ProhibitTimer is started in the first TTI of an SR                bundle.

5.7 Discontinuous Reception (DRX)

The MAC entity may be configured by RRC with a DRX functionality thatcontrols the UE's PDCCH monitoring activity for the MAC entity's C-RNTI,TPC-PUCCH-RNTI, TPC-PUSCH-RNTI, Semi-Persistent Scheduling C-RNTI (ifconfigured), UL Semi-Persistent Scheduling V-RNTI (if configured),eIMTA-RNTI (if configured), SL-RNTI (if configured), SL-V-RNTI (ifconfigured), CC-RNTI (if configured), SRS-TPC-RNTI (if configured), andAUL C-RNTI (if configured). When in RRC_CONNECTED, if DRX is configured,the MAC entity is allowed to monitor the PDCCH discontinuously using theDRX operation specified in this subclause; otherwise the MAC entitymonitors the PDCCH continuously. When using DRX operation, the MACentity shall also monitor PDCCH according to requirements found in othersubclauses of this specification. RRC controls DRX operation byconfiguring the timers onDurationTimer, drx-InactivityTimer,drx-Retransmission Timer (for HARQ processes scheduled using 1 ms TTI,one per DL HARQ process except for the broadcast process),drx-RetransmissionTimerShortTTI (for HARQ processes scheduled usingshort TTI, one per DL HARQ process), drx-ULRetransmissionTimer (for HARQprocesses scheduled using 1 ms TTI, one per asynchronous UL HARQprocess), drx-ULRetransmissionTimerShortTTI (for HARQ processesscheduled using short TTI, one per asynchronous UL HARQ process), thelongDRX-Cycle, the value of the drxStartOffset and optionally thedrxShortCycleTimer and shortDRX-Cycle. A HARQ RTT timer per DL HARQprocess (except for the broadcast process) and UL HARQ RTT Timer perasynchronous UL HARQ process is also defined (see subclause 7.7).When a DRX cycle is configured, the Active Time includes the time while:

-   -   onDurationTimer or drx-InactivityTimer or drx-Retransmission        Timer or drx-RetransmissionTimerShortTTI or        drx-ULRetransmissionTimer or drx-ULRetransmissionTimerShortTTI        or mac-ContentionResolutionTimer (as described in subclause        5.1.5) is running; or    -   a Scheduling Request is sent on PUCCH/SPUCCH and is pending (as        described in subclause 5.4.4); or    -   an uplink grant for a pending HARQ retransmission can occur and        there is data in the corresponding HARQ buffer for synchronous        HARQ process; or    -   a PDCCH indicating a new transmission addressed to the C-RNTI of        the MAC entity has not been received after successful reception        of a Random Access Response for the preamble not selected by the        MAC entity (as described in subclause 5.1.4); or    -   mpdcch-UL-HARQ-ACK-FeedbackConfig is configured and repetitions        within a bundle are being transmitted according to        UL_REPETITION_NUMBER.        When DRX is configured, the MAC entity shall for each subframe:    -   if a HARQ RTT Timer expires in this subframe:        -   if the data of the corresponding HARQ process was not            successfully decoded:            -   start the drx-Retransmission Timer or                drx-RetransmissionTimerShortTTI for the corresponding                HARQ process;        -   if NB-IoT, start or restart the drx-InactivityTimer.    -   if an UL HARQ RTT Timer expires in this subframe:        -   start the drx-ULRetransmissionTimer or            drx-ULRetransmissionTimerShortTTI for the corresponding HARQ            process.        -   if NB-IoT, start or restart the drx-InactivityTimer.    -   if a DRX Command MAC control element or a Long DRX Command MAC        control element is received:        -   stop onDurationTimer;        -   stop drx-InactivityTimer.    -   if drx-InactivityTimer expires or a DRX Command MAC control        element is received in this subframe:        -   if the Short DRX cycle is configured:            -   start or restart drxShortCycleTimer;            -   use the Short DRX Cycle.        -   else:            -   use the Long DRX cycle.    -   if drxShortCycleTimer expires in this subframe:        -   use the Long DRX cycle.    -   if a Long DRX Command MAC control element is received:        -   stop drxShortCycleTimer;        -   use the Long DRX cycle.    -   If the Short DRX Cycle is used and [(SFN*10)+subframe number]        modulo (shortDRX-Cycle)=(drxStartOffset) modulo        (shortDRX-Cycle); or    -   if the Long DRX Cycle is used and [(SFN*10)+subframe number]        modulo (longDRX-Cycle)=drxStartOffset:        -   if NB-IoT:            -   if there is at least one HARQ process for which neither                HARQ RTT Timer nor UL HARQ RTT Timer is running, start                onDurationTimer.        -   else:            -   start onDurationTimer.    -   during the Active Time, for a PDCCH-subframe, if the subframe is        not required for uplink transmission for half-duplex FDD UE        operation, and if the subframe is not a half-duplex guard        subframe [7] and if the subframe is not part of a configured        measurement gap and if the subframe is not part of a configured        Sidelink Discovery Gap for Reception, and for NB-IoT if the        subframe is not required for uplink transmission or downlink        reception other than on PDCCH; or    -   during the Active Time, for a subframe other than a        PDCCH-subframe and for a UE capable of simultaneous reception        and transmission in the aggregated cells, if the subframe is a        downlink subframe indicated by a valid eIMTA L1 signalling for        at least one serving cell not configured with schedulingCellId        [8] and if the subframe is not part of a configured measurement        gap and if the subframe is not part of a configured Sidelink        Discovery Gap for Reception; or    -   during the Active Time, for a subframe other than a        PDCCH-subframe and for a UE not capable of simultaneous        reception and transmission in the aggregated cells, if the        subframe is a downlink subframe indicated by a valid eIMTA L1        signalling for the SpCell and if the subframe is not part of a        configured measurement gap and if the subframe is not part of a        configured Sidelink Discovery Gap for Reception:        -   monitor the PDCCH;        -   if the PDCCH indicates a DL transmission or if a DL            assignment has been configured for this subframe:            -   if the UE is an NB-IoT UE, a BL UE or a UE in enhanced                coverage:            -   start the HARQ RTT Timer for the corresponding HARQ                process in the subframe containing the last repetition                of the corresponding PDSCH reception;            -   else:            -   start the HARQ RTT Timer for the corresponding HARQ                process;            -   stop the drx-Retransmission Timer or                drx-RetransmissionTimerShortTTI for the corresponding                HARQ process.            -   if NB-IoT, stop drx-ULRetransmissionTimer for all UL                HARQ processes.    -   if the PDCCH indicates an UL transmission for an asynchronous        HARQ process or if an UL grant has been configured for an        asynchronous HARQ process for this subframe, or if the PDCCH        indicates an UL transmission for an autonomous HARQ process or;    -   if the uplink grant is a configured grant for the MAC entity's        AUL C-RNTI and if the corresponding PUSCH transmission has been        performed in this subframe:        -   if mpdcch-UL-HARQ-ACK-FeedbackConfig is not configured; or        -   if mpdcch-UL-HARQ-ACK-FeedbackConfig is configured and an UL            HARQ-ACK feedback has not been received on PDCCH until the            last repetition of the corresponding PUSCH transmission        -   start the UL HARQ RTT Timer for the corresponding HARQ            process in the subframe containing the last repetition of            the corresponding PUSCH transmission;        -   stop the drx-ULRetransmissionTimer or            drx-ULRetransmissionTimerShortTTI for the corresponding HARQ            process;        -   if NB-IoT, stop drx-Retransmission Timer for all DL HARQ            processes.    -   if the PDCCH indicates a new transmission (DL, UL or SL):        -   except for an NB-IoT UE configured with a single DL and UL            HARQ process, start or restart drx-InactivityTimer.    -   if the PDCCH indicates a transmission (DL, UL) for an NB-IoT UE:        -   if the NB-IoT UE is configured with a single DL and UL HARQ            process:        -   stop drx-InactivityTimer.        -   stop onDurationTimer.    -   if the PDCCH indicates an UL HARQ-ACK feedback for an        asynchronous UL HARQ process for a UE configured with        mpdcch-UL-HARQ-ACK-FeedbackConfig; and    -   if the PUSCH transmission is completed:        -   stop drx-ULRetransmissionTimer for all UL HARQ processes.    -   if the PDCCH indicates HARQ feedback for one or more HARQ        processes for which UL HARQ operation is autonomous:        -   stop the drx-ULRetransmissionTimer for the corresponding            HARQ process(es).    -   in current subframe n, if the MAC entity would not be in Active        Time considering grants/assignments/DRX Command MAC control        elements/Long DRX Command MAC control elements received and        Scheduling Request sent until and including subframe n−5 when        evaluating all DRX Active Time conditions as specified in this        subclause, type-0-triggered SRS [2] shall not be reported.    -   if CQI masking (cqi-Mask) is setup by upper layers:        -   in current TTI n, if onDurationTimer would not be running            considering grants/assignments/DRX Command MAC control            elements/Long DRX Command MAC control elements received            until and including TTI n−5 when evaluating all DRX Active            Time conditions as specified in this subclause,            CQI/PMI/RI/PTI/CRI on PUCCH shall not be reported.    -   else:        -   in current TTI n, if the MAC entity would not be in Active            Time considering grants/assignments/DRX Command MAC control            elements/Long DRX Command MAC control elements received and            Scheduling Request sent until and including TTI n−5 when            evaluating all DRX Active Time conditions as specified in            this subclause, CQI/PMI/RI/PTI/CRI on PUCCH shall not be            reported.            Regardless of whether the MAC entity is monitoring PDCCH or            not, the MAC entity receives and transmits HARQ feedback and            transmits type-1-triggered SRS [2] when such is expected.            The MAC entity monitors PDCCH addressed to CC-RNTI for a            PUSCH trigger B [2] on the corresponding SCell even if the            MAC entity is not in Active Time. when such is expected.            When the BL UE or the UE in enhanced coverage or NB-IoT UE            receives PDCCH, the UE executes the corresponding action            specified in this subclause in the subframe following the            subframe containing the last repetition of the PDCCH            reception where such subframe is determined by the starting            subframe and the DCI subframe repetition number field in the            PDCCH specified in TS36.213 [2], unless explicitly stated            otherwise.    -   NOTE 1: The same Active Time applies to all activated serving        cell(s).    -   NOTE 2: In case of downlink spatial multiplexing, if a TB is        received while the HARQ RTT Timer is running and the previous        transmission of the same TB was received at least N subframes        before the current subframe (where N corresponds to the HARQ RTT        Timer), the MAC entity should process it and restart the HARQ        RTT Timer.    -   NOTE 3: The MAC entity does not consider PUSCH trigger B [2] to        be an indication of a new transmission.    -   NOTE 4: For NB-IoT, for operation in FDD mode, and for operation        in TDD mode with a single HARQ process, DL and UL transmissions        will not be scheduled in parallel, i.e. if a DL transmission has        been scheduled an UL transmission will not be scheduled until        HARQ RTT Timer of the DL HARQ process has expired (and vice        versa).

5.14 SL-SCH Data Transfer 5.14.1 SL-SCH Data Transmission 5.14.1.1 SLGrant Reception and SCI Transmission

In order to transmit on the SL-SCH the MAC entity must have at least onesidelink grant.Sidelink grants are selected as follows for sidelink communication:

-   -   if the MAC entity is configured to receive a single sidelink        grant dynamically on the PDCCH and more data is available in        STCH than can be transmitted in the current SC period, the MAC        entity shall:        -   using the received sidelink grant determine the set of            subframes in which transmission of SCI and transmission of            first transport block occur according to subclause 14.2.1 of            [2];        -   consider the received sidelink grant to be a configured            sidelink grant occurring in those subframes starting at the            beginning of the first available SC Period which starts at            least 4 subframes after the subframe in which the sidelink            grant was received, overwriting a previously configured            sidelink grant occurring in the same SC period, if            available;        -   clear the configured sidelink grant at the end of the            corresponding SC Period;    -   else, if the MAC entity is configured by upper layers to receive        multiple sidelink grants dynamically on the PDCCH and more data        is available in STCH than can be transmitted in the current SC        period, the MAC entity shall for each received sidelink grant:        -   using the received sidelink grant determine the set of            subframes in which transmission of SCI and transmission of            first transport block occur according to subclause 14.2.1 of            [2];        -   consider the received sidelink grant to be a configured            sidelink grant occurring in those subframes starting at the            beginning of the first available SC Period which starts at            least 4 subframes after the subframe in which the sidelink            grant was received, overwriting a previously configured            sidelink grant received in the same subframe number but in a            different radio frame as this configured sidelink grant            occurring in the same SC period, if available;        -   clear the configured sidelink grant at the end of the            corresponding SC Period;    -   else, if the MAC entity is configured by upper layers to        transmit using one or multiple pool(s) of resources as indicated        in subclause 5.10.4 of [8] and more data is available in STCH        than can be transmitted in the current SC period, the MAC entity        shall for each sidelink grant to be selected:        -   if configured by upper layers to use a single pool of            resources:            -   select that pool of resources for use;        -   else, if configured by upper layers to use multiple pools of            resources:            -   select a pool of resources for use from the pools of                resources configured by upper layers whose associated                priority list includes the priority of the highest                priority of the sidelink logical channel in the MAC PDU                to be transmitted;            -   NOTE: If more than one pool of resources has an                associated priority list which includes the priority of                the sidelink logical channel with the highest priority                in the MAC PDU to be transmitted, it is left for UE                implementation which one of those pools of resources to                select.        -   randomly select the time and frequency resources for SL-SCH            and SCI of a sidelink grant from the selected resource pool.            The random function shall be such that each of the allowed            selections [2] can be chosen with equal probability;        -   use the selected sidelink grant to determine the set of            subframes in which transmission of SCI and transmission of            first transport block occur according to subclause 14.2.1 of            [2];        -   consider the selected sidelink grant to be a configured            sidelink grant occurring in those subframes starting at the            beginning of the first available SC Period which starts at            least 4 subframes after the subframe in which the sidelink            grant was selected;        -   clear the configured sidelink grant at the end of the            corresponding SC Period;            -   NOTE: Retransmissions on SL-SCH cannot occur after the                configured sidelink grant has been cleared.            -   NOTE: If the MAC entity is configured by upper layers to                transmit using one or multiple pool(s) of resources as                indicated in subclause 5.10.4 of [8], it is left for UE                implementation how many sidelink grants to select within                one SC period taking the number of sidelink processes                into account.                Sidelink grants are selected as follows for V2X sidelink                communication:    -   if the MAC entity is configured to receive a sidelink grant        dynamically on the PDCCH and data is available in STCH, the MAC        entity shall:        -   use the received sidelink grant to determine the number of            HARQ retransmissions and the set of subframes in which            transmission of SCI and SL-SCH occur according to subclause            14.2.1 and 14.1.1.4A of [2];        -   consider the received sidelink grant to be a configured            sidelink grant;    -   if the MAC entity is configured by upper layers to receive a        sidelink grant on the PDCCH addressed to SL Semi-Persistent        Scheduling V-RNTI, the MAC entity shall for each SL SPS        configuration:        -   if PDCCH contents indicate SPS activation:            -   use the received sidelink grant to determine the number                of HARQ retransmissions and the set of subframes in                which transmission of SCI and SL-SCH occur according to                subclause 14.2.1 and 14.1.1.4A of [2];            -   consider the received sidelink grant to be a configured                sidelink grant;        -   if PDCCH contents indicate SPS release:            -   clear the corresponding configured sidelink grant;    -   if the MAC entity is configured by upper layers to transmit        using pool(s) of resources in one or multiple carriers as        indicated in subclause 5.10.13.1 of [8] based on sensing, or        partial sensing, or random selection only if upper layers        indicates that transmissions of multiple MAC PDUs are allowed        according to subclause 5.10.13.1a of [8], and the MAC entity        selects to create a configured sidelink grant corresponding to        transmissions of multiple MAC PDUs, and data is available in        STCH associated with one or multiple carriers, the MAC entity        shall for each Sidelink process configured for multiple        transmissions on a selected carrier according to subclause        5.14.1.5:        -   if SL_RESOURCE_RESELECTION_COUNTER=0 and when            SL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC            entity randomly selected, with equal probability, a value in            the interval [0, 1] which is above the probability            configured by upper layers in probResourceKeep; or        -   if neither transmission nor retransmission has been            performed by the MAC entity on any resource indicated in the            configured sidelink grant during the last second; or        -   if sl-ReselectAfter is configured and the number of            consecutive unused transmission opportunities on resources            indicated in the configured sidelink grant is equal to            sl-ReselectAfter; or        -   if there is no configured sidelink grant; or        -   if the configured sidelink grant cannot accommodate a RLC            SDU by using the maximum allowed MCS configured by upper            layers in maxMCS-PSSCH and the MAC entity selects not to            segment the RLC SDU; or            -   NOTE: If the configured sidelink grant cannot                accommodate the RLC SDU, it is left for UE                implementation whether to perform segmentation or                sidelink resource reselection.        -   if transmission(s) with the configured sidelink grant cannot            fulfil the latency requirement of the data in a sidelink            logical channel according to the associated PPPP, and the            MAC entity selects not to perform transmission(s)            corresponding to a single MAC PDU; or            -   NOTE: If the latency requirement is not met, it is left                for UE implementation whether to perform transmission(s)                corresponding to single MAC PDU or sidelink resource                reselection.        -   if a pool of resources is configured or reconfigured by            upper layers for the selected carrier:            -   clear the configured sidelink grant, if available;            -   trigger the TX carrier (re-)selection procedure as                specified in sub-clause 5.14.1.5;        -   if the carrier is (re-)selected in the Tx carrier            (re-)selection according to sub-clause 5.14.1.5, the            following is performed on the selected carrier:            -   select one of the allowed values configured by upper                layers in restrictResourceReservationPeriod and set the                resource reservation interval by multiplying 100 with                the selected value;            -   NOTE: How the UE selects this value is up to UE                implementation.            -   randomly select, with equal probability, an integer                value in the interval [5, 15] for the resource                reservation interval higher than or equal to 100 ms, in                the interval [10, 30] for the resource reservation                interval equal to 50 ms or in the interval [25, 75] for                the resource reservation interval equal to 20 ms, and                set SL_RESOURCE_RESELECTION_COUNTER to the selected                value;            -   select the number of HARQ retransmissions from the                allowed numbers that are configured by upper layers in                allowedRetxNumberPSSCH included in pssch-TxConfigList                and, if configured by upper layers, overlapped in                allowedRetxNumberPSSCH indicated in                cbr-pssch-TxConfigList for the highest priority of the                sidelink logical channel(s) allowed on the selected                carrier and the CBR measured by lower layers according                to [6] if CBR measurement results are available or the                corresponding defaultTxConfigIndex configured by upper                layers if CBR measurement results are not available;            -   select an amount of frequency resources within the range                that is configured by upper layers between                minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH                included in pssch-TxConfigList and, if configured by                upper layers, overlapped between                minSubchannel-NumberPSSCH and maxSubchannel-NumberPSSCH                indicated in cbr-pssch-TxConfigList for the highest                priority of the sidelink logical channel(s) allowed on                the selected carrier and the CBR measured by lower                layers according to [6] if CBR measurement results are                available or the corresponding defaultTxConfigIndex                configured by upper layers if CBR measurement results                are not available;            -   if transmission based on random selection is configured                by upper layers:            -   randomly select the time and frequency resources for one                transmission opportunity from the resource pool,                according to the amount of selected frequency resources.                The random function shall be such that each of the                allowed selections can be chosen with equal probability;            -   else:            -   randomly select the time and frequency resources for one                transmission opportunity from the resources indicated by                the physical layer according to subclause 14.1.1.6 of                [2], according to the amount of selected frequency                resources. The random function shall be such that each                of the allowed selections can be chosen with equal                probability;            -   use the randomly selected resource to select a set of                periodic resources spaced by the resource reservation                interval for transmission opportunities of SCI and                SL-SCH corresponding to the number of transmission                opportunities of MAC PDUs determined in subclause                14.1.1.4B of [2];            -   if the number of HARQ retransmissions is equal to 1 and                there are available resources left in the resources                indicated by the physical layer that meet the conditions                in subclause 14.1.1.7 of [2] for more transmission                opportunities:            -   randomly select the time and frequency resources for one                transmission opportunity from the available resources,                according to the amount of selected frequency resources.                The random function shall be such that each of the                allowed selections can be chosen with equal probability;            -   use the randomly selected resource to select a set of                periodic resources spaced by the resource reservation                interval for the other transmission opportunities of SCI                and SL-SCH corresponding to the number of retransmission                opportunities of the MAC PDUs determined in subclause                14.1.1.4B of [2];            -   consider the first set of transmission opportunities as                the new transmission opportunities and the other set of                transmission opportunities as the retransmission                opportunities;            -   consider the set of new transmission opportunities and                retransmission opportunities as the selected sidelink                grant.            -   else:            -   consider the set as the selected sidelink grant;            -   use the selected sidelink grant to determine the set of                subframes in which transmissions of SCI and SL-SCH occur                according to subclause 14.2.1 and 14.1.1.4B of [2];            -   consider the selected sidelink grant to be a configured                sidelink grant;        -   else if SL_RESOURCE_RESELECTION_COUNTER=0 and when            SL_RESOURCE_RESELECTION_COUNTER was equal to 1 the MAC            entity randomly selected, with equal probability, a value in            the interval [0, 1] which is less than or equal to the            probability configured by upper layers in probResourceKeep:            -   clear the configured sidelink grant, if available;            -   randomly select, with equal probability, an integer                value in the interval [5, 15] for the resource                reservation interval higher than or equal to 100 ms, in                the interval [10, 30] for the resource reservation                interval equal to 50 ms or in the interval [25, 75] for                the resource reservation interval equal to 20 ms, and                set SL_RESOURCE_RESELECTION_COUNTER to the selected                value;            -   use the previously selected sidelink grant for the                number of transmissions of the MAC PDUs determined in                subclause 14.1.1.4B of [2] with the resource reservation                interval to determine the set of subframes in which                transmissions of SCI and SL-SCH occur according to                subclause 14.2.1 and 14.1.1.4B of [2];            -   consider the selected sidelink grant to be a configured                sidelink grant;        -   else, if the MAC entity is configured by upper layers to            transmit using pool(s) of resources in one or multiple            carriers as indicated in subclause 5.10.13.1 of [8], the MAC            entity selects to create a configured sidelink grant            corresponding to transmission(s) of a single MAC PDU, and            data is available in STCH associated with one or multiple            carriers, the MAC entity shall for a Sidelink process on a            selected carrier according to subclause 5.14.1.5:            -   trigger the TX carrier (re-)selection procedure as                specified in sub-clause 5.14.1.5;            -   if the carrier is (re-)selected in the Tx carrier                (re-)selection according to sub-clause 5.14.1.5, the                following is performed on the selected carrier:                -   select the number of HARQ retransmissions from the                    allowed numbers that are configured by upper layers                    in allowedRetxNumberPSSCH included in                    pssch-TxConfigList and, if configured by upper                    layers, overlapped in allowedRetxNumberPSSCH                    indicated in cbr-pssch-TxConfigList for the highest                    priority of the sidelink logical channel(s) allowed                    on the selected carrier and the CBR measured by                    lower layers according to [6] if CBR measurement                    results are available or the corresponding                    defaultTxConfigIndex configured by upper layers if                    CBR measurement results are not available;                -   select an amount of frequency resources within the                    range that is configured by upper layers between                    minSubchannel-NumberPSSCH and                    maxSubchannel-NumberPSSCH included in                    pssch-TxConfigList and, if configured by upper                    layers, overlapped between minSubchannel-NumberPSSCH                    and maxSubchannel-NumberPSSCH indicated in                    cbr-pssch-TxConfigList for the highest priority of                    the sidelink logical channel(s) allowed on the                    selected carrier and the CBR measured by lower                    layers according to [6] if CBR measurement results                    are available or the corresponding                    defaultTxConfigIndex configured by upper layers if                    CBR measurement results are not available;                -   if transmission based on random selection is                    configured by upper layers:                -   randomly select the time and frequency resources for                    one transmission opportunity of SCI and SL-SCH from                    the resource pool, according to the amount of                    selected frequency resources. The random function                    shall be such that each of the allowed selections                    can be chosen with equal probability;                -   else:                -   randomly select the time and frequency resources for                    one transmission opportunity of SCI and SL-SCH from                    the resources indicated by the physical layer                    according to subclause 14.1.1.6 of [2], according to                    the amount of selected frequency resources. The                    random function shall be such that each of the                    allowed selections can be chosen with equal                    probability;                -   if the number of HARQ retransmissions is equal to 1:                -   if transmission based on random selection is                    configured by upper layers and there are available                    resources that meet the conditions in subclause                    14.1.1.7 of [2] for one more transmission                    opportunity:                -   randomly select the time and frequency resources for                    the other transmission opportunity of SCI and SL-SCH                    corresponding to additional transmission of the MAC                    PDU from the available resources, according to the                    amount of selected frequency resources. The random                    function shall be such that each of the allowed                    selections can be chosen with equal probability;            -   else, if transmission based on sensing or partial                sensing is configured by upper layers and there are                available resources left in the resources indicated by                the physical layer that meet the conditions in subclause                14.1.1.7 of [2] for one more transmission opportunity:                -   randomly select the time and frequency resources for                    the other transmission opportunity of SCI and SL-SCH                    corresponding to additional transmission of the MAC                    PDU from the available resources, according to the                    amount of selected frequency resources. The random                    function shall be such that each of the allowed                    selections can be chosen with equal probability;            -   consider a transmission opportunity which comes first in                time as the new transmission opportunity and a                transmission opportunity which comes later in time as                the retransmission opportunity;            -   consider both of the transmission opportunities as the                selected sidelink grant;            -   else:            -   consider the transmission opportunity as the selected                sidelink grant;            -   use the selected sidelink grant to determine the                subframes in which transmission(s) of SCI and SL-SCH                occur according to subclause 14.2.1 and 14.1.1.4B of                [2];            -   consider the selected sidelink grant to be a configured                sidelink grant.            -   NOTE: For V2X sidelink communication, the UE should                ensure the randomly selected time and frequency                resources fulfill the latency requirement.            -   NOTE: For V2X sidelink communication, when there is no                overlapping between the chosen configuration(s) in                pssch-TxConfigList and chosen configuration(s) indicated                in cbr-pssch-TxConfigList, it is up to UE implementation                whether the UE transmits and which transmitting                parameters the UE uses between allowed configuration(s)                indicated in pssch-TxConfigList and allowed                configuration(s) indicated in cbr-pssch-TxConfigList.                The MAC entity shall for each subframe:    -   if the MAC entity has a configured sidelink grant occurring in        this subframe:        -   if SL_RESOURCE_RESELECTION_COUNTER=1 and the MAC entity            randomly selected, with equal probability, a value in the            interval [0, 1] which is above the probability configured by            upper layers in probResourceKeep:            -   set the resource reservation interval equal to 0;        -   if the configured sidelink grant corresponds to transmission            of SCI:            -   for V2X sidelink communication in UE autonomous resource                selection:            -   select a MCS which is, if configured, within the range                that is configured by upper layers between minMCS-PSSCH                and maxMCS-PSSCH included in pssch-TxConfigList and, if                configured by upper layers, overlapped between                minMCS-PSSCH and maxMCS-PSSCH indicated in                cbr-pssch-TxConfigList for the highest priority of the                sidelink logical channel(s) in the MAC PDU and the CBR                measured by lower layers according to [6] if CBR                measurement results are available or the corresponding                defaultTxConfigIndex configured by upper layers if CBR                measurement results are not available;                -   NOTE: MCS selection is up to UE implementation if                    the MCS or the corresponding range is not configured                    by upper layers.                -   NOTE: For V2X sidelink communication, when there is                    no overlapping between the chosen configuration(s)                    included in pssch-TxConfigList and chosen                    configuration(s) indicated in                    cbr-pssch-TxConfigList, it is up to UE                    implementation whether the UE transmits and which                    transmitting parameters the UE uses between allowed                    configuration(s) indicated in pssch-TxConfigList and                    allowed configuration(s) indicated in                    cbr-pssch-TxConfigList.            -   for V2X sidelink communication in scheduled resource                allocation:            -   select a MCS unless it is configured by upper layer;            -   instruct the physical layer to transmit SCI                corresponding to the configured sidelink grant;            -   for V2X sidelink communication, deliver the configured                sidelink grant, the associated HARQ information and the                value of the highest priority of the sidelink logical                channel(s) in the MAC PDU to the Sidelink HARQ Entity                for this subframe;        -   else if the configured sidelink grant corresponds to            transmission of first transport block for sidelink            communication:            -   deliver the configured sidelink grant and the associated                HARQ information to the Sidelink HARQ Entity for this                subframe.            -   NOTE: If the MAC entity has multiple configured grants                occurring in one subframe and if not all of them can be                processed due to the single-cluster SC-FDM restriction,                it is left for UE implementation which one of these to                process according to the procedure above.

5.14.1.2 Sidelink HARQ Operation 5.14.1.2.1 Sidelink HARQ Entity

The MAC entity is configured by upper layers to transmit using pool(s)of resources on one or multiple carriers as indicated in subclause5.10.13.1 of 3GPP TS 36.331 [8], there is one Sidelink HARQ Entity atthe MAC entity for each carrier for transmission on SL-SCH, whichmaintains a number of parallel Sidelink processes.For sidelink communication, the number of transmitting Sidelinkprocesses associated with the Sidelink HARQ Entity is defined in [8].For V2X sidelink communication, the maximum number of transmittingSidelink processes associated with each Sidelink HARQ Entity is 8. Asidelink process may be configured for transmissions of multiple MACPDUs. For transmissions of multiple MAC PDUs, the maximum number oftransmitting Sidelink processes associated with each Sidelink HARQEntity is 2.A delivered and configured sidelink grant and its associated HARQinformation are associated with a Sidelink process.For each subframe of the SL-SCH and each Sidelink process, the SidelinkHARQ Entity shall:

-   -   if a sidelink grant corresponding to a new transmission        opportunity has been indicated for this Sidelink process and        there is SL data, for sidelink logical channels of ProSe        destination associated with this sidelink grant, available for        transmission:        -   obtain the MAC PDU from the “Multiplexing and assembly”            entity;        -   deliver the MAC PDU and the sidelink grant and the HARQ            information to this Sidelink process;        -   instruct this Sidelink process to trigger a new            transmission.    -   else, if this subframe corresponds to retransmission opportunity        for this Sidelink process:        -   instruct this Sidelink process to trigger a retransmission.            -   NOTE: The resources for retransmission opportunities are                specified in subclause 14.2.1 of [2] unless specified in                subclause 5.14.1.1.

5.14.1.2.2 Sidelink Process

The Sidelink process is associated with a HARQ buffer.The sequence of redundancy versions is 0, 2, 3, 1. The variableCURRENT_IRV is an index into the sequence of redundancy versions. Thisvariable is updated modulo 4.New transmissions and retransmissions either for a given SC period insidelink communication or in V2X sidelink communication are performed onthe resource indicated in the sidelink grant as specified in subclause5.14.1.1 and with the MCS selected as specified in subclause 5.14.1.1.If the sidelink process is configured to perform transmissions ofmultiple MAC PDUs for V2X sidelink communication the process maintains acounter SL_RESOURCE_RESELECTION_COUNTER. For other configurations of thesidelink process, this counter is not available.If the Sidelink HARQ Entity requests a new transmission, the Sidelinkprocess shall:

-   -   set CURRENT_IRV to 0;    -   store the MAC PDU in the associated HARQ buffer;    -   store the sidelink grant received from the Sidelink HARQ Entity;    -   generate a transmission as described below.        If the Sidelink HARQ Entity requests a retransmission, the        Sidelink process shall:    -   generate a transmission as described below.        To generate a transmission, the Sidelink process shall:    -   if there is no uplink transmission; or if the MAC entity is able        to perform uplink transmissions and transmissions on SL-SCH        simultaneously at the time of the transmission; or if there is a        MAC PDU to be transmitted in this TTI in uplink, except a MAC        PDU obtained from the Msg3 buffer and transmission of V2X        sidelink communication is prioritized over uplink transmission;        and    -   if there is no Sidelink Discovery Gap for Transmission or no        transmission on PSDCH at the time of the transmission; or, in        case of transmissions of V2X sidelink communication, if the MAC        entity is able to perform transmissions on SL-SCH and        transmissions on PSDCH simultaneously at the time of the        transmission:        -   instruct the physical layer to generate a transmission            according to the stored sidelink grant with the redundancy            version corresponding to the CURRENT_IRV value.    -   increment CURRENT_IRV by 1;    -   if this transmission corresponds to the last transmission of the        MAC PDU:        -   decrement SL_RESOURCE_RESELECTION_COUNTER by 1, if            available.            The transmission of V2X sidelink communication is            prioritized over uplink transmission if the following            conditions are met:    -   if the MAC entity is not able to perform uplink transmissions        and transmissions of V2X sidelink communication simultaneously        at the time of the transmission; and    -   if uplink transmission is not prioritized by upper layer        according to [15]; and    -   if the value of the highest priority of the sidelink logical        channel(s) in the MAC PDU is lower than thresSL-TxPrioritization        if thresSL-TxPrioritization is configured.

5.14.1.3 Multiplexing and Assembly

For PDU(s) associated with one SCI, MAC shall consider only logicalchannels with the same Source Layer-2 ID-Destination Layer-2 ID pair.Multiple transmissions within overlapping SC periods to different ProSeDestinations are allowed subject to single-cluster SC-FDM constraint.In V2X sidelink communication, multiple transmissions for differentSidelink processes are allowed to be independently performed indifferent subframes.

5.14.1.3.1 Logical Channel Prioritization

The Logical Channel Prioritization procedure is applied when a newtransmission is performed. Each sidelink logical channel has anassociated priority which is the PPPP and optionally an associated PPPR.Multiple sidelink logical channels may have the same associatedpriority. The mapping between priority and LCID is left for UEimplementation. If duplication is activated as specified in 3GPP TS36.323 [4], the MAC entity shall map different sidelink logical channelswhich correspond to the same PDCP entity in duplication onto differentcarriers in accordance with 5.14.1.5 or onto different carriers ofdifferent carrier set, if configured by upper layer (3GPP TS 36.331[8]), based on UE implementation.The MAC entity shall perform the following Logical ChannelPrioritization procedure either for each SCI transmitted in an SC periodin sidelink communication, or for each SCI corresponding to a newtransmission in V2X sidelink communication:

-   -   The MAC entity shall allocate resources to the sidelink logical        channels in the following steps:        -   Only consider sidelink logical channels not previously            selected for this SC period and the SC periods (if any)            which are overlapping with this SC period, to have data            available for transmission in sidelink communication;        -   Only consider sidelink logical channels which meet the            following conditions:            -   allowed on the carrier where the SCI is transmitted for                V2X sidelink communication, if the carrier is configured                by upper layers according to 3GPP TS 36.331 [8] and 3GPP                TS 24.386 [15];            -   having a priority whose associated                threshCBR-FreqReselection is no lower than the CBR of                the carrier when the carrier is (re-)selected in                accordance with 5.14.1.5;        -   Exclude sidelink logical channel(s) not allowed on the            carrier where the SCI is transmitted, if duplication is            activated as specified in 3GPP TS 36.323 [4].        -   Step 0: Select a ProSe Destination, having the sidelink            logical channel with the highest priority, among the            sidelink logical channels having data available for            transmission and having the same transmission format as the            one selected corresponding to the ProSe Destination;            -   NOTE: The sidelink logical channels belonging to the                same ProSe Destination have the same transmission                format.    -   For each MAC PDU associated to the SCI:        -   Step 1: Among the sidelink logical channels belonging to the            selected ProSe Destination and having data available for            transmission, allocate resources to the sidelink logical            channel with the highest priority;        -   Step 2: if any resources remain, sidelink logical channels            belonging to the selected ProSe Destination are served in            decreasing order of priority until either the data for the            sidelink logical channel(s) or the SL grant is exhausted,            whichever comes first. Sidelink logical channels configured            with equal priority should be served equally.    -   The UE shall also follow the rules below during the scheduling        procedures above:        -   the UE should not segment an RLC SDU (or partially            transmitted SDU) if the whole SDU (or partially transmitted            SDU) fits into the remaining resources;        -   if the UE segments an RLC SDU from the sidelink logical            channel, it shall maximize the size of the segment to fill            the grant as much as possible;        -   the UE should maximise the transmission of data;        -   if the MAC entity is given a sidelink grant size that is            equal to or larger than 10 bytes (for sidelink            communication) or 11 bytes (for V2X sidelink communication)            while having data available for transmission, the MAC entity            shall not transmit only padding.

5.14.1.3.2 Multiplexing of MAC SDUs

The MAC entity shall multiplex MAC SDUs in a MAC PDU according tosubclauses 5.14.1.3.1 and 6.1.6.

5.14.1.4 Buffer Status Reporting

The sidelink Buffer Status reporting procedure is used to provide theserving eNB with information about the amount of sidelink data availablefor transmission in the SL buffers associated with the MAC entity. RRCcontrols BSR reporting for the sidelink by configuring the two timersperiodic-BSR-TimerSL and retx-BSR-TimerSL. Each sidelink logical channelbelongs to a ProSe Destination. Each sidelink logical channel isallocated to an LCG depending on the priority and optionally the PPPR ofthe sidelink logical channel, and the mapping between LCG ID andpriority and optionally the mapping between LCG ID and PPPR which areprovided by upper layers in logicalChGroupinfoList [8]. LCG is definedper ProSe Destination.A sidelink Buffer Status Report (BSR) shall be triggered if any of thefollowing events occur:

-   -   if the MAC entity has a configured SL-RNTI or a configured        SL-V-RNTI:        -   SL data, for a sidelink logical channel of a ProSe            Destination, becomes available for transmission in the RLC            entity or in the PDCP entity (the definition of what data            shall be considered as available for transmission is            specified in [3] and [4] respectively) and either the data            belongs to a sidelink logical channel with higher priority            than the priorities of the sidelink logical channels which            belong to any LCG belonging to the same ProSe Destination            and for which data is already available for transmission, or            there is currently no data available for transmission for            any of the sidelink logical channels belonging to the same            ProSe Destination, in which case the Sidelink BSR is            referred below to as “Regular Sidelink BSR”;        -   UL resources are allocated and number of padding bits            remaining after a Padding BSR has been triggered is equal to            or larger than the size of the Sidelink BSR MAC control            element containing the buffer status for at least one LCG of            a ProSe Destination plus its subheader, in which case the            Sidelink BSR is referred below to as “Padding Sidelink BSR”;        -   retx-BSR-TimerSL expires and the MAC entity has data            available for transmission for any of the sidelink logical            channels, in which case the Sidelink BSR is referred below            to as “Regular Sidelink BSR”;        -   periodic-BSR-TimerSL expires, in which case the Sidelink BSR            is referred below to as “Periodic Sidelink BSR”;    -   else:        -   An SL-RNTI or an SL-V-RNTI is configured by upper layers and            SL data is available for transmission in the RLC entity or            in the PDCP entity (the definition of what data shall be            considered as available for transmission is specified in [3]            and [4] respectively), in which case the Sidelink BSR is            referred below to as “Regular Sidelink BSR”.

For Regular and Periodic Sidelink BSR:

-   -   if the number of bits in the UL grant is equal to or larger than        the size of a Sidelink BSR containing buffer status for all LCGs        having data available for transmission plus its subheader:        -   report Sidelink BSR containing buffer status for all LCGs            having data available for transmission;    -   else report Truncated Sidelink BSR containing buffer status for        as many LCGs having data available for transmission as possible,        taking the number of bits in the UL grant into consideration.

For Padding Sidelink BSR:

-   -   if the number of padding bits remaining after a Padding BSR has        been triggered is equal to or larger than the size of a Sidelink        BSR containing buffer status for all LCGs having data available        for transmission plus its subheader:        -   report Sidelink BSR containing buffer status for all LCGs            having data available for transmission;    -   else report Truncated Sidelink BSR containing buffer status for        as many LCGs having data available for transmission as possible,        taking the number of bits in the UL grant into consideration.        If the Buffer Status reporting procedure determines that at        least one Sidelink BSR has been triggered and not cancelled:    -   if the MAC entity has UL resources allocated for new        transmission for this TTI and the allocated UL resources can        accommodate a Sidelink BSR MAC control element plus its        subheader as a result of logical channel prioritization:        -   instruct the Multiplexing and Assembly procedure to generate            the Sidelink BSR MAC control element(s);        -   start or restart periodic-BSR-TimerSL except when all the            generated Sidelink BSRs are Truncated Sidelink BSRs;        -   start or restart retx-BSR-TimerSL;    -   else if a Regular Sidelink BSR has been triggered:        -   if an uplink grant is not configured:            -   a Scheduling Request shall be triggered.                A MAC PDU shall contain at most one Sidelink BSR MAC                control element, even when multiple events trigger a                Sidelink BSR by the time a Sidelink BSR can be                transmitted in which case the Regular Sidelink BSR and                the Periodic Sidelink BSR shall have precedence over the                padding Sidelink BSR.                The MAC entity shall restart retx-BSR-TimerSL upon                reception of an SL grant.                All triggered regular Sidelink BSRs shall be cancelled                in case the remaining configured SL grant(s) valid for                this SC Period can accommodate all pending data                available for transmission in sidelink communication or                in case the remaining configured SL grant(s) valid can                accommodate all pending data available for transmission                in V2X sidelink communication. All triggered Sidelink                BSRs shall be cancelled in case the MAC entity has no                data available for transmission for any of the sidelink                logical channels. All triggered Sidelink BSRs shall be                cancelled when a Sidelink BSR (except for Truncated                Sidelink BSR) is included in a MAC PDU for transmission.                All triggered Sidelink BSRs shall be cancelled, and                retx-BSR-TimerSL and periodic-BSR-TimerSL shall be                stopped, when upper layers configure autonomous resource                selection.                The MAC entity shall transmit at most one                Regular/Periodic Sidelink BSR in a TTI. If the MAC                entity is requested to transmit multiple MAC PDUs in a                TTI, it may include a padding Sidelink BSR in any of the                MAC PDUs which do not contain a Regular/Periodic                Sidelink BSR.                All Sidelink BSRs transmitted in a TTI always reflect                the buffer status after all MAC PDUs have been built for                this TTI. Each LCG shall report at the most one buffer                status value per TTI and this value shall be reported in                all Sidelink BSRs reporting buffer status for this LCG.    -   NOTE: A Padding Sidelink BSR is not allowed to cancel a        triggered Regular/Periodic Sidelink BSR. A Padding Sidelink BSR        is triggered for a specific MAC PDU only and the trigger is        cancelled when this MAC PDU has been built.

6.1.3.1a Sidelink BSR MAC Control Elements

Sidelink BSR and Truncated Sidelink BSR MAC control elements consist ofone Destination Index field, one LCG ID field and one correspondingBuffer Size field per reported target group. The Sidelink BSR MACcontrol elements are identified by MAC PDU subheaders with LCIDs asspecified in table 6.2.1-2. They have variable sizes.For each included group, the fields are defined as follows (FIGS.6.1.3.1 a-1 and 6.1.3.1 a-2):

-   -   Destination Index: The Destination Index field identifies the        ProSe Destination or the destination for V2X sidelink        communication. The length of this field is 4 bits. The value is        set to the index of the destination reported in        destinationInfoList for sidelink communication or is set to one        index among index(es) associated to same destination reported in        v2x-DestinationInfoList for V2X sidelink communication. If        multiple such lists are reported, the value is indexed        sequentially across all the lists in the same order as specified        in [8];    -   LCG ID: The Logical Channel Group ID field identifies the group        of logical channel(s) which buffer status is being reported. The        length of the field is 2 bits;    -   Buffer Size: The Buffer Size field identifies the total amount        of data available across all logical channels of a LCG of a        ProSe Destination after all MAC PDUs for the TTI have been        built. The amount of data is indicated in number of bytes. It        shall include all data that is available for transmission in the        RLC layer and in the PDCP layer; the definition of what data        shall be considered as available for transmission is specified        in [3] and [4] respectively. The size of the RLC and MAC headers        are not considered in the buffer size computation. The length of        this field is 6 bits. The values taken by the Buffer Size field        are shown in Table 6.1.3.1-1;    -   R: Reserved bit, set to “0”.        Buffer Sizes of LCGs are included in decreasing order of the        highest priority of the sidelink logical channel belonging to        the LCG irrespective of the value of the Destination Index        field.        FIG. 5 (a reproduction of FIG. 6.1.3.1 a-1: Sidelink BSR and        Truncated Sidelink BSR MAC control element for even N).        FIG. 6 (a reproduction of FIG. 6.1.3.1 a-2: Sidelink BSR and        Truncated Sidelink BSR MAC control element for odd N).

6.1.6 Mac Pdu (Sl-Sch)

A MAC PDU consists of a MAC header, one or more MAC Service Data Units(MAC SDU), and optionally padding; as described in FIG. 6.1.6-4.Both the MAC header and the MAC SDUs are of variable sizes.A MAC PDU header consists of one SL-SCH subheader, one or more MAC PDUsubheaders; each subheader except SL-SCH subheader corresponds to eithera MAC SDU or padding.The SL-SCH subheader consists of the seven header fieldsV/R/R/R/R/SRC/DST.A MAC PDU subheader consists of the six header fields R/R/E/LCID/F/L butfor the last subheader in the MAC PDU. The last subheader in the MAC PDUconsists solely of the four header fields R/R/E/LCID. A MAC PDUsubheader corresponding to padding consists of the four header fieldsR/R/E/LCID.FIG. 7 (a reproduction of FIG. 6.1.6-1: R/R/E/LCID/F/L MAC subheader).FIG. 8 (a reproduction of FIG. 6.1.6-2: R/R/E/LCID MAC subheader).FIG. 9 (a reproduction of FIG. 6.1.6-3: SL-SCH MAC subheader forV=“0001” and “0010”).FIG. 10 (a reproduction of FIG. 6.1.6-3 a: SL-SCH MAC subheader forV=″0011″).MAC PDU subheaders have the same order as the corresponding MAC SDUs andpadding.Padding occurs at the end of the MAC PDU, except when single-byte ortwo-byte padding is required. Padding may have any value and the MACentity shall ignore it. When padding is performed at the end of the MACPDU, zero or more padding bytes are allowed.When single-byte or two-byte padding is required, one or two MAC PDUsubheaders corresponding to padding are placed after the SL-SCHsubheader and before any other MAC PDU subheader.A maximum of one MAC PDU can be transmitted per TB.FIG. 11 (a reproduction of FIG. 6.1.6-4: Example of MAC PDU consistingof MAC header, MAC SDUs and padding).

In 3GPP TS 38.321-f40, Scheduling Request (SR), Buffer Status Reporting(BSR), and Discontinuous Reception (DRX) mechanism in New Radio (NR) isquoted below:

5.4.4 Scheduling Request

The Scheduling Request (SR) is used for requesting UL-SCH resources fornew transmission.The MAC entity may be configured with zero, one, or more SRconfigurations. An SR configuration consists of a set of PUCCH resourcesfor SR across different BWPs and cells. For a logical channel, at mostone PUCCH resource for SR is configured per BWP.Each SR configuration corresponds to one or more logical channels. Eachlogical channel may be mapped to zero or one SR configuration, which isconfigured by RRC. The SR configuration of the logical channel thattriggered the BSR (subclause 5.4.5) (if such a configuration exists) isconsidered as corresponding SR configuration for the triggered SR.RRC configures the following parameters for the scheduling requestprocedure:

-   -   sr-ProhibitTimer (per SR configuration);    -   sr-TransMax (per SR configuration).        The following UE variables are used for the scheduling request        procedure:    -   SR_COUNTER (per SR configuration).        If an SR is triggered and there are no other SRs pending        corresponding to the same SR configuration, the MAC entity shall        set the SR_COUNTER of the corresponding SR configuration to 0.        When an SR is triggered, it shall be considered as pending until        it is cancelled. All pending SR(s) triggered prior to the MAC        PDU assembly shall be cancelled and each respective        sr-ProhibitTimer shall be stopped when the MAC PDU is        transmitted and this PDU includes a Long or Short BSR MAC CE        which contains buffer status up to (and including) the last        event that triggered a BSR (see subclause 5.4.5) prior to the        MAC PDU assembly. All pending SR(s) shall be cancelled and each        respective sr-ProhibitTimer shall be stopped when the UL        grant(s) can accommodate all pending data available for        transmission.        Only PUCCH resources on a BWP which is active at the time of SR        transmission occasion are considered valid.        As long as at least one SR is pending, the MAC entity shall for        each pending SR:    -   1> if the MAC entity has no valid PUCCH resource configured for        the pending SR:        -   2> initiate a Random Access procedure (see subclause 5.1) on            the SpCell and cancel the pending SR.    -   1> else, for the SR configuration corresponding to the pending        SR:        -   2> when the MAC entity has an SR transmission occasion on            the valid PUCCH resource for SR configured; and        -   2> if sr-ProhibitTimer is not running at the time of the SR            transmission occasion; and        -   2> if the PUCCH resource for the SR transmission occasion            does not overlap with a measurement gap; and        -   2> if the PUCCH resource for the SR transmission occasion            does not overlap with a UL-SCH resource:            -   3> if SR_COUNTER<sr-TransMax:                -   4> increment SR_COUNTER by 1;                -   4> instruct the physical layer to signal the SR on                    one valid PUCCH resource for SR;                -   4> start the sr-ProhibitTimer.            -   3> else:                -   4> notify RRC to release PUCCH for all Serving                    Cells;                -   4> notify RRC to release SRS for all Serving Cells;                -   4> clear any configured downlink assignments and                    uplink grants;                -   4> clear any PUSCH resources for semi-persistent CSI                    reporting;                -   4> initiate a Random Access procedure (see subclause                    5.1) on the SpCell and cancel all pending SRs.    -   NOTE 1: The selection of which valid PUCCH resource for SR to        signal SR on when the MAC entity has more than one overlapping        valid PUCCH resource for the SR transmission occasion is left to        UE implementation.    -   NOTE 2: If more than one individual SR triggers an instruction        from the MAC entity to the PHY layer to signal the SR on the        same valid PUCCH resource, the SR_COUNTER for the relevant SR        configuration is incremented only once.        The MAC entity may stop, if any, ongoing Random Access procedure        due to a pending SR which has no valid PUCCH resources        configured, which was initiated by MAC entity prior to the MAC        PDU assembly. Such a Random Access procedure may be stopped when        the MAC PDU is transmitted using a UL grant other than a UL        grant provided by Random Access Response, and this PDU includes        a BSR MAC CE which contains buffer status up to (and including)        the last event that triggered a BSR (see subclause 5.4.5) prior        to the MAC PDU assembly, or when the UL grant(s) can accommodate        all pending data available for transmission.

5.4.5 Buffer Status Reporting

The Buffer Status reporting (BSR) procedure is used to provide theserving gNB with information about UL data volume in the MAC entity.RRC configures the following parameters to control the BSR:

-   -   periodicBSR-Timer;    -   retxBSR-Timer;    -   logicalChannelSR-DelayTimerApplied;    -   logicalChannelSR-DelayTimer;    -   logicalChannelSR-Mask;    -   logicalChannelGroup.        Each logical channel may be allocated to an LCG using the        logicalChannelGroup. The maximum number of LCGs is eight.        The MAC entity determines the amount of UL data available for a        logical channel according to the data volume calculation        procedure in TSs 38.322 [3] and 38.323 [4].        A BSR shall be triggered if any of the following events occur:    -   UL data, for a logical channel which belongs to an LCG, becomes        available to the MAC entity; and either        -   this UL data belongs to a logical channel with higher            priority than the priority of any logical channel containing            available UL data which belong to any LCG; or        -   none of the logical channels which belong to an LCG contains            any available UL data. in which case the BSR is referred            below to as ‘Regular BSR’;    -   UL resources are allocated and number of padding bits is equal        to or larger than the size of the Buffer Status Report MAC CE        plus its subheader, in which case the BSR is referred below to        as ‘Padding BSR’;    -   retxBSR-Timer expires, and at least one of the logical channels        which belong to an LCG contains UL data, in which case the BSR        is referred below to as ‘Regular BSR’;    -   periodicBSR-Timer expires, in which case the BSR is referred        below to as ‘Periodic BSR’.    -   NOTE: When Regular BSR triggering events occur for multiple        logical channels simultaneously, each logical channel triggers        one separate Regular BSR.        For Regular BSR, the MAC entity shall:    -   1> if the BSR is triggered for a logical channel for which        logicalChannelSR-DelayTimerApplied is configured by upper        layers:        -   2> start or restart the logicalChannelSR-DelayTimer.    -   1> else:        -   2> if running, stop the logicalChannelSR-DelayTimer.            For Regular and Periodic BSR, the MAC entity shall:    -   1> if more than one LCG has data available for transmission when        the MAC PDU containing the BSR is to be built:        -   2> report Long BSR for all LCGs which have data available            for transmission.    -   1> else:        -   2> report Short BSR.

For Padding BSR:

-   -   1> if the number of padding bits is equal to or larger than the        size of the Short BSR plus its subheader but smaller than the        size of the Long BSR plus its subheader:        -   2> if more than one LCG has data available for transmission            when the BSR is to be built:            -   3> if the number of padding bits is equal to the size of                the Short BSR plus its subheader:                -   4> report Short Truncated BSR of the LCG with the                    highest priority logical channel with data available                    for transmission.            -   3> else:                -   4> report Long Truncated BSR of the LCG(s) with the                    logical channels having data available for                    transmission following a decreasing order of the                    highest priority logical channel (with or without                    data available for transmission) in each of these                    LCG(s), and in case of equal priority, in increasing                    order of LCGID.        -   2> else:            -   3> report Short BSR.    -   1> else if the number of padding bits is equal to or larger than        the size of the Long BSR plus its subheader:        -   2> report Long BSR for all LCGs which have data available            for transmission.            For BSR triggered by retxBSR-Timer expiry, the MAC entity            considers that the logical channel that triggered the BSR is            the highest priority logical channel that has data available            for transmission at the time the BSR is triggered.            The MAC entity shall:    -   1> if the Buffer Status reporting procedure determines that at        least one BSR has been triggered and not cancelled:        -   2> if UL-SCH resources are available for a new transmission            and the UL-SCH resources can accommodate the BSR MAC CE plus            its subheader as a result of logical channel prioritization:            -   3> instruct the Multiplexing and Assembly procedure to                generate the BSR MAC CE(s);            -   3> start or restart periodicBSR-Timer except when all                the generated BSRs are long or short Truncated BSRs;            -   3> start or restart retxBSR-Timer.        -   2> if a Regular BSR has been triggered and            logicalChannelSR-DelayTimer is not running:            -   3> if there is no UL-SCH resource available for a new                transmission; or            -   3> if the MAC entity is configured with configured                uplink grant(s) and the Regular BSR was triggered for a                logical channel for which logicalChannelSR-Mask is set                to false; or 3> if the UL-SCH resources available for a                new transmission do not meet the LCP mapping                restrictions (see subclause 5.4.3.1) configured for the                logical channel that triggered the BSR:                -   4> trigger a Scheduling Request.    -   NOTE: UL-SCH resources are considered available if the MAC        entity has an active configuration for either type of configured        uplink grants, or if the MAC entity has received a dynamic        uplink grant, or if both of these conditions are met. If the MAC        entity has determined at a given point in time that UL-SCH        resources are available, this need not imply that UL-SCH        resources are available for use at that point in time.        A MAC PDU shall contain at most one BSR MAC CE, even when        multiple events have triggered a BSR. The Regular BSR and the        Periodic BSR shall have precedence over the padding BSR.        The MAC entity shall restart retxBSR-Timer upon reception of a        grant for transmission of new data on any UL-SCH.        All triggered BSRs may be cancelled when the UL grant(s) can        accommodate all pending data available for transmission but is        not sufficient to additionally accommodate the BSR MAC CE plus        its subheader. All BSRs triggered prior to MAC PDU assembly        shall be cancelled when a MAC PDU is transmitted and this PDU        includes a Long or Short BSR MAC CE which contains buffer status        up to (and including) the last event that triggered a BSR prior        to the MAC PDU assembly.    -   NOTE: MAC PDU assembly can happen at any point in time between        uplink grant reception and actual transmission of the        corresponding MAC PDU. BSR and SR can be triggered after the        assembly of a MAC PDU which contains a BSR MAC CE, but before        the transmission of this MAC PDU. In addition, BSR and SR can be        triggered during MAC PDU assembly.

5.7 Discontinuous Reception (DRX)

The MAC entity may be configured by RRC with a DRX functionality thatcontrols the UE's PDCCH monitoring activity for the MAC entity's C-RNTI,CS-RNTI, INT-RNTI, SFI-RNTI, SP-CSI-RNTI, TPC-PUCCH-RNTI,TPC-PUSCH-RNTI, and TPC-SRS-RNTI. When using DRX operation, the MACentity shall also monitor PDCCH according to requirements found in othersubclauses of this specification. When in RRC_CONNECTED, if DRX isconfigured, for all the activated Serving Cells, the MAC entity maymonitor the PDCCH discontinuously using the DRX operation specified inthis subclause; otherwise the MAC entity shall monitor the PDCCHcontinuously.RRC controls DRX operation by configuring the following parameters:

-   -   drx-onDurationTimer: the duration at the beginning of a DRX        Cycle;    -   drx-SlotOffset: the delay before starting the        drx-onDurationTimer;    -   drx-InactivityTimer: the duration after the PDCCH occasion in        which a PDCCH indicates a new UL or DL transmission for the MAC        entity;    -   drx-RetransmissionTimerDL (per DL HARQ process except for the        broadcast process): the maximum duration until a DL        retransmission is received;    -   drx-RetransmissionTimerUL (per UL HARQ process): the maximum        duration until a grant for UL retransmission is received;    -   drx-LongCycleStartOffset: the Long DRX cycle and drx-StartOffset        which defines the subframe where the Long and Short DRX Cycle        starts;    -   drx-ShortCycle (optional): the Short DRX cycle;    -   drx-ShortCycleTimer (optional): the duration the UE shall follow        the Short DRX cycle;    -   drx-HARQ-RTT-TimerDL (per DL HARQ process except for the        broadcast process): the minimum duration before a DL assignment        for HARQ retransmission is expected by the MAC entity;    -   drx-HARQ-RTT-TimerUL (per UL HARQ process): the minimum duration        before a UL HARQ retransmission grant is expected by the MAC        entity.        When a DRX cycle is configured, the Active Time includes the        time while:    -   drx-onDurationTimer or drx-InactivityTimer or        drx-RetransmissionTimerDL or drx-RetransmissionTimerUL or        ra-ContentionResolutionTimer (as described in subclause 5.1.5)        is running; or    -   a Scheduling Request is sent on PUCCH and is pending (as        described in subclause 5.4.4); or    -   a PDCCH indicating a new transmission addressed to the C-RNTI of        the MAC entity has not been received after successful reception        of a Random Access Response for the Random Access Preamble not        selected by the MAC entity among the contention-based Random        Access Preamble (as described in subclause 5.1.4).        When DRX is configured, the MAC entity shall:    -   1> if a MAC PDU is received in a configured downlink assignment:        -   2> start the drx-HARQ-RTT-TimerDL for the corresponding HARQ            process in the first symbol after the end of the            corresponding transmission carrying the DL HARQ feedback;        -   2> stop the drx-RetransmissionTimerDL for the corresponding            HARQ process.    -   1> if a MAC PDU is transmitted in a configured uplink grant:        -   2> start the drx-HARQ-RTT-TimerUL for the corresponding HARQ            process in the first symbol after the end of the first            repetition of the corresponding PUSCH transmission;        -   2> stop the drx-RetransmissionTimerUL for the corresponding            HARQ process.    -   1> if a drx-HARQ-RTT-TimerDL expires:        -   2> if the data of the corresponding HARQ process was not            successfully decoded:            -   3> start the drx-RetransmissionTimerDL for the                corresponding HARQ process in the first symbol after the                expiry of drx-HARQ-RTT-TimerDL.    -   1> if a drx-HARQ-RTT-TimerUL expires:        -   2> start the drx-RetransmissionTimerUL for the corresponding            HARQ process in the first symbol after the expiry of            drx-HARQ-RTT-TimerUL.    -   1> if a DRX Command MAC CE or a Long DRX Command MAC CE is        received:        -   2> stop drx-onDurationTimer;        -   2> stop drx-InactivityTimer.    -   1> if drx-InactivityTimer expires or a DRX Command MAC CE is        received:        -   2> if the Short DRX cycle is configured:            -   3> start or restart drx-ShortCycleTimer in the first                symbol after the expiry of drx-InactivityTimer or in the                first symbol after the end of DRX Command MAC CE                reception;            -   3> use the Short DRX Cycle.        -   2> else:            -   3> use the Long DRX cycle.    -   1> if drx-ShortCycleTimer expires:        -   2> use the Long DRX cycle.    -   1> if a Long DRX Command MAC CE is received:        -   2> stop drx-ShortCycleTimer;        -   2> use the Long DRX cycle.    -   1> if the Short DRX Cycle is used, and [(SFN×10)+subframe        number] modulo (drx-ShortCycle)=(drx-StartOffset) modulo        (drx-ShortCycle); or    -   1> if the Long DRX Cycle is used, and [(SFN×10)+subframe number]        modulo (drx-LongCycle)=drx-Start Offset:        -   2> start drx-onDurationTimer after drx-SlotOffset from the            beginning of the subframe.    -   1> if the MAC entity is in Active Time:        -   2> monitor the PDCCH;        -   2> if the PDCCH indicates a DL transmission:            -   3> start the drx-HARQ-RTT-TimerDL for the corresponding                HARQ process in the first symbol after the end of the                corresponding transmission carrying the DL HARQ                feedback;            -   3> stop the drx-RetransmissionTimerDL for the                corresponding HARQ process.        -   2> if the PDCCH indicates a UL transmission:            -   3> start the drx-HARQ-RTT-TimerUL for the corresponding                HARQ process in the first symbol after the end of the                first repetition of the corresponding PUSCH                transmission;            -   3> stop the drx-RetransmissionTimerUL for the                corresponding HARQ process.        -   2> if the PDCCH indicates a new transmission (DL or UL):            -   3> start or restart drx-InactivityTimer in the first                symbol after the end of the PDCCH reception.    -   1> in current symbol n, if the MAC entity would not be in Active        Time considering grants/assignments/DRX Command MAC CE/Long DRX        Command MAC CE received and Scheduling Request sent 4 ms prior        to symbol n when evaluating all DRX Active Time conditions as        specified in this subclause:        -   2> not transmit periodic SRS and semi-persistent SRS defined            in TS 38.214 [7].    -   1> if CSI masking (csi-Mask) is setup by upper layers:        -   2> in current symbol n, if onDurationTimer would not be            running considering grants/assignments/DRX Command MAC            CE/Long DRX Command MAC CE received 4 ms prior to symbol n            when evaluating all DRX Active Time conditions as specified            in this subclause:            -   3> not report CSI on PUCCH.    -   1> else:        -   2> in current symbol n, if the MAC entity would not be in            Active Time considering grants/assignments/DRX Command MAC            CE/Long DRX Command MAC CE received and Scheduling Request            sent 4 ms prior to symbol n when evaluating all DRX Active            Time conditions as specified in this subclause:            -   3> not report CSI on PUCCH and semi-persistent CSI on                PUSCH.                Regardless of whether the MAC entity is monitoring PDCCH                or not, the MAC entity transmits HARQ feedback,                aperiodic CSI on PUSCH, and aperiodic SRS defined in TS                38.214 [7] when such is expected.                The MAC entity needs not to monitor the PDCCH if it is                not a complete PDCCH occasion (e.g. the Active Time                starts or ends in the middle of a PDCCH occasion).

In RAN1 #94 chairman's note, the agreements of NR Vehicle-to-Everything(V2X) are discussed and quoted below:

Agreements:

At least two sidelink resource allocation modes are defined for NR-V2Xsidelink communication

-   -   Mode 1: Base station schedules sidelink resource(s) to be used        by UE for sidelink transmission(s)    -   Mode 2: UE determines (i.e. base station does not schedule)        sidelink transmission resource(s) within sidelink resources        configured by base station/network or pre-configured sidelink        resources

Notes:

-   -   eNB control of NR sidelink and gNB control of LTE sidelink        resources will be separately considered in corresponding agenda        items.    -   Mode-2 definition covers potential sidelink radio-layer        functionality or resource allocation sub-modes (subject to        further refinement including merging of some or all of them)        where    -   a) UE autonomously selects sidelink resource for transmission    -   b) UE assists sidelink resource selection for other UE(s)    -   c) UE is configured with NR configured grant (type-1 like) for        sidelink transmission    -   d) UE schedules sidelink transmissions of other UEs        RAN1 to continue study details of resource allocation modes for        NR-V2X sidelink communication

In RAN1 #adohoc1901, the agreements for how a UE to request sidelinkresource for retransmission are discussed and quoted below:

Agreements:

-   -   It is supported that in mode 1 for unicast, the in-coverage UE        sends an indication to gNB to indicate the need for        retransmission        -   At least PUCCH is used to report the information            -   If feasible, RAN1 reuses PUCCH defined in Rel-15        -   The gNB can also schedule re-transmission resource        -   FFS transmitter UE and/or receiver UE            -   If receiver UE, the indication is in the form of HARQ                ACK/NAK            -   If transmitter UE, FFS

Some or all of the following terminology and assumption may be usedhereafter.

-   -   BS: a network central unit or a network node in NR which is used        to control one or multiple TRPs which are associated with one or        multiple cells. Communication between BS and TRP(s) is via        fronthaul. BS may be referred to as central unit (CU), eNB, gNB,        or NodeB.    -   TRP: a transmission and reception point provides network        coverage and directly communicates with UEs. TRP may be referred        to as distributed unit (DU) or network node.    -   Cell: a cell is composed of one or multiple associated TRPs,        i.e. coverage of the cell is composed of coverage of all        associated TRP(s). One cell is controlled by one BS. Cell may be        referred to as TRP group (TRPG).    -   For network side:    -   Downlink timing of TRPs in the same cell are synchronized.    -   RRC layer of network side is in BS.        For UE side:    -   There are at least two UE (RRC) states: connected state (or        called active state) and non-connected state (or called inactive        state or idle state). Inactive state may be an additional state        or belong to connected state or non-connected state.

Based on the current RAN1 design, a UE performing a sidelink unicastcommunication will support HARQ feedback in a sidelink interface. Inother words, a Transmit (Tx) UE will monitor HARQ feedback from aReceive (Rx) UE after the Tx UE performed a sidelink transmission to theRx UE. Based on the HARQ feedback result, the Tx UE may need to use thesidelink resource to perform a retransmission for the sidelinktransmission to the Rx UE again through the sidelink interface.

Currently, in the RAN1 discussion, the Tx UE (i.e., Mode 1 UE) may needto transmit an indication to the base station to indicate the need forretransmission. In the discussion, the indication could be one or moreHARQ feedbacks for indicating whether a transmission of a sidelink grantis successful or unsuccessful. And it would be possible for a UE toreceive another sidelink grant or a sidelink grant for retransmissionfor responding to such indication/HARQ feedback. Based on current NewRadio (NR) Discontinuous Reception (DRX) design or LTEVehicle-to-Everything (V2X) design, the UE may stay in a DRX period andwill not receive any downlink control signaling from the Base Station(BS). In such case, the BS may need to wait until the next on-durationperiod to schedule the another Sidelink (SL) grant or the SL grant forretransmission as shown in FIG. 12. The gray area is the delay time thatthe UE will not monitor the downlink control channel (e.g., PhysicalDownlink Control Channel (PDCCH), coreset, and/or a PDCCH occasion).

Considering the possible DRX configuration, another SL grant or the SLgrant for retransmission may not be able to satisfy the latencyrequirement of data included in the sidelink transmission. Although theBS could improve latency by configuring a short DRX period to the UE,the UE could suffer from a longer awaking time and increase unnecessarypower consumption.

The following methods address this issue. As those skilled in the artwill appreciate, one or more of the following methods may be applied atthe same time.

According to one method, a new active time for monitoring a sidelinkgrant and/or a sidelink grant for retransmission after/in response totransmitting a feedback of the sidelink transmission to a BS forindicating the need for retransmission. In this method, the UE startsmonitoring a sidelink grant and/or a sidelink grant for retransmissionafter/in response to the UE transmitting a feedback of a sidelinktransmission. In one method, the BS configures whether the UE shouldstart monitoring sidelink grants. In one method, the start timing of themonitoring period is configured by a BS (e.g., controlled by a timer ora counter). Alternatively, the start timing of the monitoring period ispredefined or preconfigured. In addition, the UE monitors the sidelinkgrant and/or the sidelink grant for retransmission within a monitoringperiod. In one method, the monitoring period is controlled by a timer ora counter. In one method, a length of the monitoring period isconfigured by a BS. Alternatively, the length of the monitoring periodis preconfigured or predefined in the UE.

In one embodiment, the UE starts/triggers a sidelink retransmissiontimer after the UE transmits the feedback of a sidelink transmission(e.g., a retransmission request indication) to the BS. In one method,the UE will start a Round-Trip Time (RTT) timer (for sidelink) after thetransmission feedback of the sidelink transmission and before start ofthe sidelink retransmission timer. In one method, the RTT timer (forsidelink) is used for triggering/starting the sidelink retransmissiontimer and the sidelink retransmission timer is triggered/started by theUE after the RTT timer expires. In one method, a length of the RTT timeris configured by a BS. Alternatively, the length of the RTT timer ispredefined. In another method, the RTT timer is maintained in a per UEmanner. Alternatively, the RTT timer is maintained in per sidelink HARQprocess manner. In one method, the RTT timer is different and/orindependent from a RTT timer used for uplink and/or downlink.Alternatively, the RTT timer is the same timer or the shared same valueas the RTT timer used for the uplink HARQ process. In one method, thesidelink retransmission timer is different and/or independent from aretransmission timer used for uplink and/or downlink. Alternatively, thesidelink retransmission timer is the same timer or the shared same valueas the retransmission timer used for the uplink HARQ process.

Alternatively, the UE directly starts the sidelink retransmission timerin response to the transmission of the feedback of the sidelinktransmission to the BS.

In another method, the sidelink retransmission timer is maintained in aper UE manner. Alternatively, the sidelink retransmission timer ismaintained in a per sidelink HARQ process manner. Alternatively, thesidelink retransmission timer is a per sidelink HARQ process used forsidelink unicast communication or for a sidelink communication whichneeds HARQ feedback.

In another embodiment, a new condition for starting or restarting aninactivity timer (e.g. drx-InactivityTimer) is defined. In anothermethod, the feedback of the sidelink transmission could start or restartthe inactivity timer and keep the UE monitoring the PDCCH for sidelinkgrant and/or sidelink grant for retransmission. In another method, a UEstarts or restarts the inactivity timer when the UE receives a sidelinkgrant for retransmission. Accordingly, the UE can prolong the possiblescheduling time for the base station. In one method, the above-mentionedinactivity timer is the drx-InactivityTimer disclosed in 3GPP TS38.321-f40. Alternatively, the above-mentioned inactivity-timer isanother inactivity-timer for the sidelink. An example for the embodimentis shown in FIG. 14. After the UE performs a transmission of aretransmission request indication (e.g., the feedback for the sidelinktransmission) to the BS, the UE starts the inactivity timer again.

For above methods and/or embodiment, the UE starts the timer and/ormonitors the downlink control channel (e.g., coreset and/or PDCCHoccasion) if the feedback of the sidelink transmission indicates aNegative Acknowledgement (NACK) or the need of a retransmission.Alternatively, the UE starts the timer and/or monitors downlink controlchannel (e.g. coreset and/or PDCCH occasion) regardless of the contentof the feedback to the BS.

According to another method, the UE uses a Scheduling Request (SR)transmission for indicating the need for retransmission. The SRtransmission is used for requesting a sidelink grant and/or a sidelinkgrant for retransmission (instead of the uplink grant). After the UEperforms the SR for a sidelink grant and/or a sidelink grant forretransmission, the UE will start to monitor the downlink controlchannel (used for scheduling the sidelink grant and/or the sidelinkgrant for retransmission). In another method, the UE has no pending SRassociated with the SR transmission.

Alternatively, if we treat a SR for the sidelink resource by the MediumAccess Control (MAC) entity following the procedure of the SR for theuplink grant, based on current specification, the UE starts monitoringthe PDCCH after the UE performs a SR transmission (for uplink) to thebase station. On the other hand, the SR transmission is triggered by apending SR. The pending SR is usually triggered by a Buffer StatusReport (BSR) or a sidelink BSR. The pending SR will be cancelled when aMAC Protocol Data Unit (PDU) is assembled. The PDU includes a SidelinkBSR which contains a buffer status up to (and including) the last eventthat triggered a Sidelink BSR. However, if the pending SR for triggeringthe SR transmission is triggered by the retransmission request (or theHARQ NACK received in the sidelink interface) instead of a triggeredsidelink BSR, then the pending SR will not be cancelled in any cases.And the pending SR will continuously trigger the SR transmission and thecaused problem.

For the pending SR not triggered by the sidelink BSR, some possible waysfor cancelling the pending SR are listed as follows. In one method, thepending SR of the SR transmission is cancelled when the UE receives asidelink grant. In another method, the pending SR of the SR transmissionis cancelled when the UE receives a sidelink grant for retransmission.In one method, the pending SR of the SR transmission is cancelled whenthe UE receives a sidelink grant corresponding to the sidelinktransmission which triggered the pending SR. In one method, the pendingSR of the SR transmission is cancelled when the Transfer Block (TB),which needs retransmission, is discarded, flushed, or overwritten.

In one method, the correspondence between a sidelink grant (or asidelink for retransmission) and the sidelink transmission beingperformed is determined by a sidelink HARQ process ID/index.Alternatively, the correspondence between a sidelink grant (or asidelink for retransmission) and the sidelink transmission beingperformed is determined by the reception timing of the sidelink grant(or a sidelink for retransmission). Alternatively, the correspondencebetween a sidelink grant (or a sidelink for retransmission) and thesidelink transmission being performed is determined by a field or anindication included in the sidelink grant (or a sidelink forretransmission). Alternatively, the correspondence between a sidelinkgrant (or a sidelink for retransmission) and the sidelink transmissionbeing performed is determined by a transport block size indicated by thesidelink grant (or a sidelink for retransmission).

In one method, a UE starts or restarts an Inactive timer when the UEreceives a sidelink grant for retransmission. By this way, it canprolong the possible scheduling time for the base station.

In one method, the UE performs the SR transmission (for sidelink) if theUE receives a NACK in a sidelink interface for a sidelink transmissionor the UE does not receive a HARQ feedback corresponding to a sidelinktransmission (which needs HARQ feedback in sidelink interface) in asidelink interface. Alternatively, the UE performs the SR transmission(for sidelink) regardless of the HARQ feedback result in the sidelinkinterface for a sidelink transmission. The UE performs the SRtransmission (for sidelink) if the SR transmission needs a HARQ feedbackresult in the sidelink interface or the UE is configured with orallocated with resource(s) for performing the SR transmission.

In one method, the UE monitors the downlink control channel (e.g.,PDCCH, PDCCH occasion, and/or coreset) in response to performing the SRtransmission (for sidelink) if the HARQ feedback result in the sidelinkinterface is a NACK or a Discontinuous Transmission (DTX) (i.e.,receives no HARQ feedback).

According to another method, the a dedicated coreset/PDCCH monitoringoccasion is allocated to receive a sidelink grant and/or sidelink grantretransmission. In NR, a concept called coreset is defined. A coreset isdesigned to limit a specific control resource set for a UE to performdecode. A smaller control resource set can reduce decoding overload in aUE, and a larger control resource set could let a BS schedule moretransmissions for improving data rates. A similar concept is a PDCCHmonitoring occasion. The fewer PDCCH monitoring occasions can reduce aUE's power consumption, and more PDCCH monitoring occasions can reducescheduling latency.

In this method, a UE will be allocated to one or multiple coresetsand/or sets of PDCCH monitoring occasions for monitoring a sidelinkgrant and/or a sidelink grant for retransmission. The balance betweenpower consumption and data rates could be controlled by a BS bydetermining the size of coreset and/or the amount of PDCCH occasions.Alternatively, the UE is allocated one or multiple coresets and/or oneor more sets of PDCCH monitoring occasions for monitoring a sidelinkgrant or a sidelink grant for retransmission.

In one method, the UE starts monitoring one or multiple coresets and/orset of PDCCH monitoring occasions in response to the transmission of theretransmission request indication to the BS.

In one method, if the coreset(s) and/or PDCCH occasion(s) are not sharedwith Uu scheduling, a UE applies another Discontinuous Reception (DRX)mechanism for the coresets and/or PDCCH occasion for controlling thepower consumption and decoding complexity. In one method, the DRXmechanism means the same procedure with different configurations (e.g.,length of timer, start offset, DRX period).

In another method, the UE does not apply the DRX mechanism to the PDCCHmonitoring of the sidelink grant and/or sidelink grant forretransmission. In one method, the UE does not apply the DRX mechanismto a Radio Network Temporary Identifier (RNTI) used for schedulingsidelink grant and/or sidelink grant for retransmission. In one method,one or multiple coresets and/or one or multiple sets of PDCCH occasionsof the sidelink grant are separated from the coresets and/or PDCCHoccasion sets used for Uu scheduling (e.g. UL grant, DL assignment).Alternatively, the coreset(s) and/or PDCCH occasion set(s) of thesidelink grant are shared or are the same as the coreset and/or PDCCHoccasions used for Uu scheduling (e.g. UL grant, DL assignment). Byremoving DRX, the UE could always be able to receive a sidelink grantand/or sidelink grant for retransmission. In one method, one or multiplecoresets and/or one or multiple set of the PDCCH occasions of thesidelink grant for retransmission are separated from the coresets and/orthe PDCCH occasion sets used for Uu scheduling (e.g. UL grant, DLassignment).

In another method, the Inactivity timer is configured with a largeenough value for covering any scheduling delay from a new transmissionuntil retransmission. In this method, the network (e.g., BS) will needto allocate a long enough timer value to cover any potential futurescheduling. Following LTE V2X design, a UE will start or restart aninactivity timer in response to receiving a sidelink grant for a newtransmission. In order to prevent issues, the network could allocate along enough inactivity timer value for scheduling a potential sidelinkgrant for retransmission or another sidelink grant. The timerelationship is shown in FIG. 13. As shown in FIG. 13, the inactivitytimer is longer than a whole round trip transmission and the processingtime in the sidelink interface. The gray area is the time for thenetwork to schedule a potential sidelink grant for retransmission oranother sidelink grant. More specifically, the inactivity timer islonger than the maximum time for a whole round trip transmission and theprocessing time for a sidelink transmission which needs the sidelinkHARQ feedback in the sidelink interface plus the processing andtransmission delay for the retransmission request indication.

In another method, the UE starts to monitor a downlink control channelwhen receiving HARQ feedback from another device in a sidelinkinterface. After a first UE performs a sidelink transmission to a secondUE through a sidelink interface, the first UE monitors a HARQ feedbackfor the sidelink transmission in the sidelink interface. The first UEneeds to transmit a feedback and/or a retransmission request indicationto a BS for indicating whether the sidelink transmission needs aretransmission. Since issues may be caused by not monitoring a downlinkcontrol channel, the first UE starts monitoring the downlink controlchannel when the first UE determines that the HARQ feedback result forthe sidelink transmission in the sidelink interface. More specifically,the first UE determines the HARQ feedback as a NACK if the first UEreceives the NACK from the second UE. The first UE determines the HARQfeedback as an ACK if the first UE receives the ACK from the second UE.The first UE determines the HARQ feedback as a NACK or DTX if the firstUE does not receive a corresponding HARQ feedback from the second UE.

In one method, the first UE starts monitoring the downlink controlchannel when the first UE determines the HARQ feedback result for thesidelink transmission in the sidelink interface as a NACK or DTX.Alternatively, the first UE starts monitoring the downlink controlchannel regardless of the HARQ feedback result.

In one method, the UE transmits the feedback and/or the retransmissionrequest indication to the BS if the UE determines the HARQ feedbackresult as a NACK or DTX. Alternatively, the UE transmits the feedbackand/or the retransmission request indication to the BS regardless of theHARQ feedback result, but the contents of or the format of the feedbackand/or the retransmission request indication will be different dependingon the HARQ feedback result.

For some of the above-disclosed methods, the UE is in RRC_CONNECTED. Inone method, the UE is configured with a network scheduling mode (i.e.,mode 1). In one method, the UE is configured with a dual mode (i.e.,both mode 1 and mode 2). In one method, the sidelink grant and thesidelink grant for retransmission have different Downlink ControlInformation (DCI) format. Alternatively, the sidelink grant and thesidelink grant for retransmission share the same DCI format. In onemethod, the sidelink transmission is or includes a sidelink datatransmission (e.g., SL-SCH, data belongs to SL logical channel). In onemethod, the sidelink transmission is a sidelink unicast transmission.Alternatively, the sidelink transmission is a sidelink groupcasttransmission. In one method, the sidelink transmission includes asidelink control information transmission.

According to one exemplary method for a first device to monitor downcontrol signal for scheduling sidelink resource, the includes:performing a sidelink transmission to a second device based on a firstsidelink grant allocated by a base station; determining a retransmissionneed of the sidelink transmission based on a first sidelink resourceused for monitoring feedback of the sidelink transmission from thesecond device; transmitting a retransmission indication for theretransmission need to the base station; and monitoring a downlinkcontrol resource set in response to the transmission of theretransmission indication.

In another exemplary method, the sidelink transmission is an unicasttransmission.

In another exemplary method, the sidelink transmission needs to receiveHARQ feedback from the second device through sidelink interface.

In another exemplary method, the first sidelink grant allocates a secondsidelink resource for the sidelink transmission.

In another exemplary method, the first sidelink grant allocates a firstuplink resource for the transmission of the retransmission indication.

In another exemplary method, the first sidelink resource is determinedby the second sidelink resource.

In another exemplary method, the first device transmits theretransmission indication to the base station if the UE does not receivethe feedback from the second device.

In another exemplary method, the first device transmits theretransmission indication to the base station if the feedback from thesecond device indicates reception failure of the sidelink transmission.

In another exemplary method, the first device starts or restarts a timerin response to the transmission of the retransmission indication,wherein the timer is used for controlling period of the monitoring.

In another exemplary method, the timer is an Inactivity-timer (e.g.drx-InactivityTimer).

In another exemplary method, the timer is a new timer different from theInactivity-timer (i.e. drx-InactivityTimer).

In another exemplary method, the downlink control resource set is aPDCCH channel.

In another exemplary method, the downlink control resource set includesa set of PDCCH occasion(s).

In another exemplary method, the downlink control resource set is acoreset.

In another exemplary method for a first device to monitor down controlsignal for scheduling sidelink resource, the method includes: performinga sidelink transmission to a second device based on a first sidelinkgrant allocated by a base station; determining a retransmission need ofthe sidelink transmission based on a first sidelink resource used formonitoring feedback of the sidelink transmission from the second device;transmitting a retransmission indication for the retransmission need tothe base station; starting a first timer in response to transmission ofthe retransmission indication; and monitoring a downlink controlresource set after the first timer expires.

In another exemplary method, the sidelink transmission is an unicasttransmission.

In another exemplary method, the sidelink transmission needs to receivea HARQ feedback from the second device through a sidelink interface.

In another exemplary method, the first sidelink grant allocates a secondsidelink resource for the sidelink transmission.

In another exemplary method, the first sidelink grant allocates a firstuplink resource for the transmission of the retransmission indication.

In another exemplary method, the first sidelink resource is determinedby the second sidelnk resource.

In another exemplary method, the first device transmits theretransmission indication to the base station if the UE does not receivethe feedback from the second device.

In another exemplary method, the first device transmits theretransmission indication to the base station if the feedback from thesecond device indicates reception failure of the sidelink transmission.

In another exemplary method, the first timer is a timer for notmonitoring the downlink control resource set.

In another exemplary method, the first timer is a timer for determiningwhen to start a second timer.

In another exemplary method, the first timer is a RTT timer (for asidelink).

In another exemplary method, the first timer is a timer for a sidelinkHARQ process.

In another exemplary method, the first device starts a second timer whenmonitoring the downlink control resource set.

In another exemplary method, the first device starts a second timer whenthe first timer expires.

In another exemplary method, the second timer is used for controlling aperiod of the monitoring.

In another exemplary method, the second timer is a timer for a sidelinkHARQ process.

In another exemplary method, the second timer is a retransmission timer(for a sidelink).

In another exemplary method, the downlink control resource set is aPDCCH channel.

In another exemplary method, the downlink control resource set includesa set of PDCCH occasion(s).

In another exemplary method, the downlink control resource set is acoreset.

In another exemplary method, the first device receives a second sidelinkgrant when monitoring the control resource set; and uses the secondsidelink grant to perform a retransmission of the sidelink transmissionto the second device.

In another exemplary method for a first device to monitor down controlsignal for scheduling sidelink resource, the method includes: triggeringa SR for a retransmission need of a sidelink transmission; performing aSR transmission for the SR to a base station; cancelling the SR whenreceiving a scheduling for the sidelink transmission; stop performing SRtransmission for the SR after the SR is cancelled.

In another exemplary method, the sidelink transmission is an unicasttransmission.

In another exemplary method, the SR is associated with a first SRconfiguration.

In another exemplary method, the association between the SR and thefirst SR configuration is configured by the base station.

In another exemplary method, the scheduling for the sidelinktransmission is a sidelink grant.

In another exemplary method, the scheduling for the sidelinktransmission is a sidelink grant for retransmission.

In another exemplary method, the first device determines the sidelinkgrant for retransmission is the scheduling for the sidelink transmissionbased on a HARQ process Index/ID indicated in the sidelink grant.

In another exemplary method, the first device determines the sidelinkgrant for retransmission is the scheduling for the sidelink transmissionbased on a received timing of the sidelink grant for retransmission.

In another exemplary method, the first device determines the sidelinkgrant for retransmission is the scheduling for the sidelink transmissionbased on a field in the sidelink grant for retransmission.

In another exemplary method, the first device determines the sidelinkgrant for retransmission is the scheduling for the sidelink transmissionbased on a transport block size field in the sidelink grant forretransmission.

In another exemplary method, the first device does not cancel the SRwhen the first device receives a first sidelink grant for a newtransmission.

In another exemplary method, the first device does not cancel the SRwhen the first device receives a second sidelink grant forretransmission, wherein the second sidelink grant is not for thesidelink transmission.

FIG. 15 is a flow chart 1500 according to one exemplary embodiment fromthe perspective of a first device such as, but not limited to, a UE,wherein the first device monitors a down control signal for schedulingsidelink resource. In step 1505, the first device performs a sidelinktransmission for a second device based on a first sidelink grantallocated by a base station. In step 1510, the first device determines aretransmission need of the sidelink transmission based on a HybridAutomatic Repeat Request (HARQ) feedback of the sidelink transmissionfrom the second device. In step 1515, the first device transmits aretransmission indication for the retransmission need to the basestation. In step 1520, the first device starts or restarts a timer uponthe transmission of the retransmission indication, wherein the timer isused for controlling a period of monitoring a downlink control resourceset.

In another method, the sidelink transmission needs to receive the HARQfeedback from the second device through a sidelink interface.

In another method, the first device transmits the retransmissionindication to the base station if the first device does not receive theHARQ feedback from the second device.

In another method, the first device transmits the retransmissionindication to the base station if the HARQ feedback from the seconddevice indicates a reception failure of the sidelink transmission.

In another method, the timer is a drx-InactivityTimer or adrx-RetransmissionTimerSL.

In another method, the downlink control resource set is a PhysicalDowlink Control Channel (PDCCH) or a coreset.

In another method, the downlink control resource set includes a set ofPDCCH occasions.

As those skilled in the art will appreciate, the various disclosedembodiments and/or methods may be combined to form new embodimentsand/or methods.

Referring back to FIGS. 3 and 4, in one embodiment, the device 300includes a program code 312 stored in memory 310, wherein the device 300monitors a down control signal for scheduling sidelink resource. The CPU308 could execute program code 312 to (i) perform a sidelinktransmission for a second device based on a first sidelink grantallocated by a base station, (ii) determine a retransmission need of thesidelink transmission based on a Hybrid Automatic Repeat Request (HARD)feedback of the sidelink transmission from the second device, (iii)transmit a retransmission indication for the retransmission need to thebase station, (iv) start or restart a timer upon the transmission of theretransmission indication, wherein the timer is used for controlling aperiod of monitoring a downlink control resource set.

Furthermore, the CPU 308 can execute the program code 312 to perform allof the above-described actions and steps or others methods describedherein.

The above-disclosed methods allow a UE to be immediately scheduled by abase station for sidelink retransmission needs.

Various aspects of the disclosure have been described above. It shouldbe apparent that the teachings herein may be embodied in a wide varietyof forms and that any specific structure, function, or both beingdisclosed herein is merely representative. Based on the teachings hereinone skilled in the art should appreciate that an aspect disclosed hereinmay be implemented independently of any other aspects and that two ormore of these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. As an exampleof some of the above concepts, in some aspects concurrent channels maybe established based on pulse repetition frequencies. In some aspectsconcurrent channels may be established based on pulse position oroffsets. In some aspects concurrent channels may be established based ontime hopping sequences.

Those of skill in the art would understand that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Those of skill would further appreciate that the various illustrativelogical blocks, modules, processors, means, circuits, and algorithmsteps described in connection with the aspects disclosed herein may beimplemented as electronic hardware (e.g., a digital implementation, ananalog implementation, or a combination of the two, which may bedesigned using source coding or some other technique), various forms ofprogram or design code incorporating instructions (which may be referredto herein, for convenience, as “software” or a “software module”), orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. Skilled artisans mayimplement the described functionality in varying ways for eachparticular application, but such implementation decisions should not beinterpreted as causing a departure from the scope of the presentdisclosure.

In addition, the various illustrative logical blocks, modules, andcircuits described in connection with the aspects disclosed herein maybe implemented within or performed by an integrated circuit (“IC”), anaccess terminal, or an access point. The IC may comprise a generalpurpose processor, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, electrical components, opticalcomponents, mechanical components, or any combination thereof designedto perform the functions described herein, and may execute codes orinstructions that reside within the IC, outside of the IC, or both. Ageneral purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

It is understood that any specific order or hierarchy of steps in anydisclosed process is an example of a sample approach. Based upon designpreferences, it is understood that the specific order or hierarchy ofsteps in the processes may be rearranged while remaining within thescope of the present disclosure. The accompanying method claims presentelements of the various steps in a sample order, and are not meant to belimited to the specific order or hierarchy presented.

The steps of a method or algorithm described in connection with theaspects disclosed herein may be embodied directly in hardware, in asoftware module executed by a processor, or in a combination of the two.A software module (e.g., including executable instructions and relateddata) and other data may reside in a data memory such as RAM memory,flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a harddisk, a removable disk, a CD-ROM, or any other form of computer-readablestorage medium known in the art. A sample storage medium may be coupledto a machine such as, for example, a computer/processor (which may bereferred to herein, for convenience, as a “processor”) such theprocessor can read information (e.g., code) from and write informationto the storage medium. A sample storage medium may be integral to theprocessor. The processor and the storage medium may reside in an ASIC.The ASIC may reside in user equipment. In the alternative, the processorand the storage medium may reside as discrete components in userequipment. Moreover, in some aspects any suitable computer-programproduct may comprise a computer-readable medium comprising codesrelating to one or more of the aspects of the disclosure. In someaspects a computer program product may comprise packaging materials.

While the invention has been described in connection with variousaspects, it will be understood that the invention is capable of furthermodifications. This application is intended to cover any variations,uses or adaptation of the invention following, in general, theprinciples of the invention, and including such departures from thepresent disclosure as come within the known and customary practicewithin the art to which the invention pertains.

What is claimed is:
 1. A method of a first device to monitor downlinkcontrol signaling for scheduling sidelink resources, comprising:performing a sidelink transmission for a second device; determining aretransmission need of the sidelink transmission based on a feedback ofthe sidelink transmission received from the second device; transmittinga retransmission indication for the retransmission need to a basestation; and starting or restarting a timer upon the transmission of theretransmission indication, wherein the timer is used for controlling around-trip time (RTT).
 2. The method of claim 1, wherein the sidelinktransmission for the second device is based on a first sidelink grantallocated by the base station.
 3. The method of claim 1, wherein thefeedback is a Hybrid Automatic Repeat Request (HARQ) feedback.
 4. Themethod of claim 3, wherein the HARQ feedback is received from the seconddevice through a sidelink interface.
 5. The method of claim 3, furthercomprising: transmitting the retransmission indication to the basestation if the first device does not receive the HARQ feedback from thesecond device.
 6. The method of claim 3, further comprising:transmitting the retransmission indication to the base station if theHARQ feedback from the second device indicates a reception failure ofthe sidelink transmission.
 7. The method of claim 1, wherein the timeris a RTT timer for sidelink.
 8. The method of claim 1, wherein thedownlink control signaling includes a Physical Downlink Control Channel(PDCCH) or a coreset.
 9. The method of claim 1, wherein the downlinkcontrol signaling includes a set of PDCCH occasions.
 10. The method ofclaim 1, wherein the timer is used for triggering start of aretransmission timer for sidelink, and for controlling a period ofmonitoring a downlink control resource set.
 11. A first deviceconfigured to monitor downlink control signaling for scheduling sidelinkresources, comprising: a memory; and a processor operatively coupled tothe memory, wherein the processor is configured to execute program codeto: perform a sidelink transmission for a second device; determine aretransmission need of the sidelink transmission based on a feedback ofthe sidelink transmission received from the second device; transmit aretransmission indication for the retransmission need to a base station;and start or restart a timer upon the transmission of the retransmissionindication, wherein the timer is used for controlling a round-trip time(RTT).
 12. The first device of claim 11, wherein the sidelinktransmission for the second device is based on a first sidelink grantallocated by the base station.
 13. The first device of claim 11, whereinthe feedback is a Hybrid Automatic Repeat Request (HARQ) feedback. 14.The first device of claim 13, wherein the HARQ feedback is received fromthe second device through a sidelink interface.
 15. The first device ofclaim 13, wherein the processor is further configured to execute programcode to: transmit the retransmission indication to the base station ifthe first device does not receive the HARQ feedback from the seconddevice.
 16. The first device of claim 13, wherein the processor isfurther configured to execute program code to: transmit theretransmission indication to the base station if the HARQ feedback fromthe second device indicates a reception failure of the sidelinktransmission.
 17. The first device of claim 11, wherein the timer is aRTT timer for sidelink.
 18. The first device of claim 11, wherein thedownlink control signaling includes a Physical Downlink Control Channel(PDCCH) or a coreset.
 19. The first device of claim 11, wherein thedownlink control signaling includes a set of PDCCH occasions.
 20. Thefirst device of claim 11, wherein the timer is used for triggering startof a retransmission timer for sidelink, and for controlling a period ofmonitoring a downlink control resource set.